Water dispersion of gel particles, producing method thereof, and image forming method

ABSTRACT

A water dispersion of gel particles, a method of producing the water dispersion, and an image forming method using the water dispersion. The gel particles have a three-dimensional crosslinked structure including a structural unit represented by Formula (1) and a urea bond, have a hydrophilic group and a polymerizable group, include photopolymerization initiators and are dispersed in water. In Formula (1), R 1  represents H or an alkyl group; X 1  represents hydrogen, halogen, a hydroxyl group, an alkyl group, a cyano group, a lactam group, a —C(═O)X 2 R 2  group, an —OC(═O)R 3  group, or an aryl group; X 2  represents oxygen or an —N(R X2 )— group; R X2  and R 2  represent a hydrocarbon group that may contain a hetero atom or H; R 2  and R X2  may be bonded to each other to form a ring, and R 3  represents a hydrocarbon group that may contain a hetero atom.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of International Application No. PCT/JP2016/052962, filed Feb. 1, 2016, the disclosure of which is incorporated herein by reference in its entirety. Further, this application claims priority from Japanese Patent Application No. 2015-061718, filed Mar. 24, 2015, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a water dispersion of gel particles, a producing method thereof, and an image forming method.

2. Description of the Related Art

Examples of the image forming method of forming an image on a recording medium include an electrophotographic method, a sublimation-type thermal transfer method, a fusion-type thermal transfer method, and an ink jet method.

For example, since the ink jet method of forming an image can be performed with a cheap device, and the ink can be effectively used, the ink jet method has an advantage in that running cost is not expensive.

Examples of the ink jet method include an image forming method obtained by using ink for ink jet that can be cured by irradiation with active energy rays such as ultraviolet rays.

Hereinafter, ink jet ink that can be cured by irradiation with active energy rays is called “photocurable ink”. In addition to ink jet ink, a composition that can be cured by irradiation with active energy rays is referred to as “photocurable composition”.

In the related art, in view of reduction of environmental burden and improvement of workability, an aqueous composition (for example, aqueous ink) including water as a solvent or a dispersion medium is used instead of a solvent-based composition (for example, solvent-based ink) including an organic solvent as a solvent or a dispersion medium.

As the aqueous photocurable composition, for example, the following compositions are known.

For example, as an ink composition for ink jet maintaining curing properties due to irradiation with ultraviolet rays in the existence of water or a solvent and having excellent jetting stability, an ink composition for ink jet including water, a colorant, a resin emulsion consisting of a compound having a radical polymerizable group, an inorganic particle dispersion, and a photoradical initiator is known (for example, see JP2013-199602A).

As an aqueous emulsion that can be thermally cured or photocured and that can be suitably used for a coating agent and the like, an aqueous emulsion containing a vinyl polymer having a specific acrylic functional group at at least one terminal is known (for example, see JP2000-136211A).

As the photocurable composition that is not limited to an aqueous composition, for example, the following compositions are known.

For example, as the colored photosensitive composition that has satisfactory color stability after exposure due to infrared laser exposure and that can obtain high color development even in a case where the exposure is performed after elapse of time, a colored photosensitive composition containing a microgel including a polymer of which a glass transition temperature is 50° C. or higher, a photoinitiator, and an infrared absorbing dye and a binder polymer is known (for example, see JP2011-213114A).

As ink for ink jet printing cured by irradiation, ink for ink jet that includes at least one irradiation curable monomer, at least one inert thermoplastic resin, at least one radical photoinitiator, and at least one colorant and that has viscosity of less than 100 mPas at 25° C., in which at least one inert resin exists by 2 to 15 weight % with respect to the total weight and has a molecular weight of 1,500 to 70,000 is known (for example, see JP2009-542833A).

SUMMARY OF THE INVENTION

Recently, it is required to form a cured film having excellent adhesiveness to the various base materials including a nonabsorbable base material (for example, a plastic base material and a metal base material).

For example, also in an ink jet-type image forming field, it is required to form an image (cured film) having excellent adhesiveness not only to paper which is an absorbable recording medium but also to a nonabsorbable recording medium.

In view of the above, in an ink composition for ink jet disclosed in JP2013-199602A, an aqueous emulsion disclosed in JP2000-136211A, and a colored photosensitive composition disclosed in JP2011-213114A, sensitivity to light tends to be insufficient, and adhesiveness to all formed cured films (images) tends to be insufficient.

In paragraph 0009 of JP2009-542833A, it is disclosed that “ink jet ink according to the present invention is mainly cured, that is, dried by polymerization of monomers existing as described above, and thus is a curable-type ink. Therefore, ink does not require the existence of water or a volatile organic solvent for drying, but these components may exist. However, it is preferable that the ink jet ink according to the present invention does not substantially include water or a volatile organic solvent.”

It is considered that respective components of the ink for ink jet disclosed in JP2009-542833A are components that are hardly dissolved or dispersed in water. Therefore, it is considered that it is difficult to prepare the ink for ink jet disclosed in JP2009-542833A as an aqueous ink composition.

An embodiment of the present invention is conceived in view of the above circumstances, and a purpose thereof is to achieve the following objects.

That is, the object of the embodiment of the present invention is to provide a water dispersion of gel particles that can form a film having excellent adhesiveness to a base material and a producing method thereof.

Another object of the embodiment of the present invention is to provide an image forming method that can form an image having excellent adhesiveness to a recording medium.

Specific means for solving the problems include the following.

<1> A water dispersion of gel particles, in which the gel particles have a three-dimensional crosslinked structure including a structural unit represented by Formula (1) and a urea bond, have a hydrophilic group and a polymerizable group, include a photopolymerization initiator and are dispersed in water,

R¹ in Formula (1) represents a hydrogen atom or an alkyl group,

X¹ in Formula (1) represents a hydrogen atom, a halogen atom, a hydroxyl group, an alkyl group, a cyano group, a lactam group, a —C(═O)X²R² group, an —OC(═O)R³ group, or an aryl group,

X² represents an oxygen atom or an —N(R^(X2))— group, and R^(X2) represents a hydrocarbon group that may contain a hetero atom or a hydrogen atom,

R² represents a hydrocarbon group that may contain a hetero atom or a hydrogen atom, provided that, in a case in which X² is an oxygen atom, R² is not a hydrogen atom,

R² and R^(X2) may be bonded to each other to form a ring, and

R³ represents a hydrocarbon group that may contain a hetero atom.

<2> The water dispersion of gel particles according to <1>,

in which, in Formula (1), R¹ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms,

X¹ is a hydrogen atom, a halogen atom, a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, a cyano group, a lactam group, a —C(═O)X²R² group, an —OC(═O)R³ group, or an aryl group,

X² is an oxygen atom or an —N(R^(X2))— group,

R^(X2) is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms,

R² is a hydrogen atom, an alkyl group having 1 to 30 carbon atoms, an alkoxyalkyl group having 2 to 30 carbon atoms, a polyalkoxyalkyl group having 3 to 30 carbon atoms, an aryloxyalkyl group having 7 to 30 carbon atoms, an aminoalkyl group having 1 to 30 carbon atoms, a monoalkylaminoalkyl group having 2 to 30 carbon atoms, or a dialkylaminoalkyl group having 3 to 30 carbon atoms, and

R³ is an alkyl group having 1 to 6 carbon atoms.

<3> The water dispersion of gel particles according to <1> or <2>, in which X¹ in Formula (1) is a —C(═O)X²R² group.

<4> The water dispersion of gel particles according to any one of <1> to <3>, in which the three-dimensional crosslinked structure includes at least one of a structural unit represented by Formula (2) or a group represented by Formula (3),

R²¹ in Formula (2) represents a hydrogen atom or an alkyl group,

L²¹ in Formula (2) represents a divalent hydrocarbon group that may contain a hetero atom,

X²¹ in Formula (2) represents an oxygen atom or a —C(═O)X²²L²²O— group,

X²² represents an oxygen atom or a —N(R^(x22))— group, and R^(x22) represents a hydrocarbon group that may contain a hetero atom,

L²² represents a divalent hydrocarbon group that may contain a hetero atom,

in Formula (2), p represents 0 or 1,

in Formula (3), Z³¹ represents a (n+1)-valent organic group and Z³² represents a (m+1)-valent organic group,

n in Formula (3) represents an integer of 1 to 4 and m represents an integer of 1 to 4, and

in Formulae (2) and (3), * represents a bonding position.

<5> The water dispersion of gel particles according to <4>,

in which, in Formula (2), R²¹ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms,

L²¹ is an alkylene group having 1 to 30 carbon atoms, an arylene group having 6 to 30 carbon atoms, an alkylene arylene group having 7 to 30 carbon atoms, an alkylene arylene alkylene group having 8 to 30 carbon atoms, an alkyleneoxyalkylene group having 2 to 30 carbon atoms, or an alkylene polyoxyalkylene group having 3 to 30 carbon atoms,

X²¹ is an oxygen atom or a —C(═O)X²²L²²O— group,

X²² is an oxygen atom or a —N(R^(x22))— group,

R^(x22) is an alkyl group having 1 to 6 carbon atoms, and

L²² is an alkylene group having 1 to 30 carbon atoms, an arylene group having 6 to 30 carbon atoms, an alkylene arylene group having 7 to 30 carbon atoms, an alkylene arylene alkylene group having 8 to 30 carbon atoms, an alkyleneoxyalkylene group having 2 to 30 carbon atoms, or an alkylene polyoxyalkylene group having 3 to 30 carbon atoms,

in Formula (3), Z³¹ is an (n+1)-valent organic group having 2 to 30 carbon atoms, and

Z³² is an (m+1)-valent organic group having 2 to 100 carbon atoms.

<6> The water dispersion of gel particles according to <4> or <5>, in which X²¹ in Formula (2) is a —C(═O)X²²L²²O— group.

<7> The water dispersion of gel particles according to any one of <1> to <6>, in which the hydrophilic group is at least one selected from the group consisting of a carboxyl group, a salt of a carboxyl group, a sulfo group, a salt of a sulfo group, a sulfate group, a salt of a sulfate group, a phosphonic acid group, a salt of a phosphonic acid group, a phosphoric acid group, a salt of a phosphoric acid group, ammonium salt group, a betaine group, and an alkyleneoxy group.

<8> The water dispersion of gel particles according to any one of <1> to <7>, in which the three-dimensional crosslinked structure includes a structural unit represented by Formula (W),

R^(W1) in Formula (W) represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms,

W¹ in Formula (W) represents a carboxyl group, a salt of the carboxyl group, a —C(═O)NH—R^(W2)—SO₃H group, a salt of a —C(═O)NH—R^(W3)—SO₃H group, a —C(═O)NH—R^(W4)—OSO₃H group, a salt of a —C(═O)NH—R^(W5)—OSO₃H group, or a —C(═O)O—(R^(W6)O)_(nw)—R^(W7) group, and

R^(W2), R^(W3), R^(W4), R^(W5), and R^(W6) each independently represent an alkylene group having 1 to 10 carbon atoms, R^(W7) represents an alkyl group having 1 to 10 carbon atoms, and nw represents an integer of 1 to 200.

<9> The water dispersion of gel particles according to any one of <1> to <8>, in which the gel particles further include a polymerizable monomer.

<10> The water dispersion of gel particles according to <9>, in which the polymerizable monomer is a (meth)acrylate monomer.

<11> The water dispersion of gel particles according to any one of <1> to <10>, in which solubility of the photopolymerization initiator in water is 1.0 mass % or less at 25° C.

<12> The water dispersion of gel particles according to any one of <1> to <11>, in which the photopolymerization initiator is an acylphosphine oxide compound.

<13> The water dispersion of gel particles according to any one of <1> to <12>, in which the gel particles further include a sensitizer.

<14> The water dispersion of gel particles according to any one of <1> to <13>, which is used for ink jet recording.

<15> The water dispersion of gel particles according to any one of <1> to <14>, in which a total solid content of the gel particles is 50 mass % or greater with respect to a total solid content of the water dispersion.

<16> The water dispersion of gel particles according to any one of <1> to <15>, in which the three-dimensional crosslinked structure includes a structure of a reaction product between water and an isocyanate group-containing polymer including a structural unit represented by Formula (1) and an isocyanate group.

<17> A method of producing the water dispersion of gel particles according to <16>, comprising:

a preparation step of preparing an isocyanate group-containing polymer including a structural unit represented by Formula (1) and an isocyanate group,

an emulsification step of obtaining an emulsion by mixing an oil phase component including the isocyanate group-containing polymer, the photopolymerization initiator, and an organic solvent, and a water phase component including water and performing emulsification, and

a gelation step of obtaining the water dispersion of gel particles by heating the emulsion to allow the isocyanate group-containing polymer and water to react with each other.

<18> An image forming method comprising: an application step of applying the water dispersion of gel particles according to any one of <1> to <16> to a recording medium; and

an irradiation step irradiating the water dispersion of gel particles applied to the recording medium with active energy rays.

An embodiment of the present invention provides a water dispersion of gel particles that can form a film having excellent adhesiveness to a base material and a producing method thereof.

An embodiment of the present invention provides an image forming method that can form an image having excellent adhesiveness to a recording medium.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Specific embodiments of the present invention are described in detail, but the present invention is not limited to the following embodiments.

In the present specification, a numerical range described by using “to” represents a range including numerical values described before and after “to” as a minimum value and a maximum value, respectively.

In the present specification, unless described otherwise, in a case where there are a plurality of substances corresponding to the respective components in a composition, an amount of each of the components in the composition means a total amount of a plurality of corresponding substances existing in the composition.

In the present specification, the term “step” does not only mean an independent step, even in a case where a step cannot be clearly differentiated from other steps, in a case where the step accomplishes a predetermined purpose, the step is included in this term.

In the present specification, “light” is a concept including γ rays, β rays, electron beams, ultraviolet rays, visible rays, and infrared rays.

In the present specification, ultraviolet rays may be referred to as “ultra violet (UV) light”.

In the present specification, light generated from a light emitting diode (LED) light source may be referred to as an “LED light”.

In the present specification, “(meth)acrylic acid” is a concept including both acrylic acid and methacrylic acid, “(meth)acrylate” is a concept including both acrylate and methacrylate, a “(meth)acryloyl group” is a concept including both an acryloyl group and a methacryloyl group.

In the present specification, “*” in a chemical formula indicates a bonding position.

[Water Dispersion of Gel Particles]

A water dispersion of gel particles (hereinafter, referred to as a “water dispersion of the present disclosure” or simply referred to as “water dispersion”) of the present disclosure is a water dispersion in which gel particles having a three-dimensional crosslinked structure including a structural unit (hereinafter, also referred to as “Unit (1)”) represented by Formula (1) and a urea bond (—NHC(═O)NH— bond), having a hydrophilic group and a polymerizable group, and including a photopolymerization initiator are dispersed in water.

R¹ in Formula (1) represents a hydrogen atom or an alkyl group.

X¹ in Formula (1) represents a hydrogen atom, a halogen atom, a hydroxyl group, an alkyl group, a cyano group, a lactam group, a —C(═O)X²R² group, an —OC(═O)R³ group, or an aryl group.

X² represents an oxygen atom or an —N(R^(X2))— group. R^(X2) represents a hydrocarbon group that may contain a hetero atom or a hydrogen atom.

R² represents a hydrocarbon group that may contain a hetero atom or a hydrogen atom. Here, in a case in which X² is an oxygen atom, R² is not a hydrogen atom.

R³ represents a hydrocarbon group that may contain a hetero atom.

In the water dispersion of the present disclosure, it is possible to form a film having excellent adhesiveness to a base material.

Specifically, in the water dispersion of the present disclosure, since the gel particles have a polymerizable group and include a photopolymerization initiator, a distance between a polymerizable group and a photopolymerization initiator becomes closer to each other, compared with a photocurable composition (for example, photocurable ink) in the related art, and thus curing sensitivity (hereinafter, simply referred to as “sensitivity”) to the irradiation with active energy rays is enhanced. Since the photopolymerization initiator is dispersed in a state of being included in the gel particles, sedimentation of the photopolymerization initiator is suppressed compared with the case where a photopolymerization initiator not included in the gel particles is dispersed, and thus excellent sensitivity is maintained. For these reasons, according to the water dispersion of the present disclosure, a film (cured film) having excellent adhesiveness to a base material can be formed.

The gel particles have a three-dimensional crosslinked structure including Unit (1) and a urea bond. This three-dimensional crosslinked structure is a firmer structure than a three-dimensional crosslinked structure not having at least one of Unit (1) or a urea bond. Since the gel particles have a corresponding firm three-dimensional crosslinked structure, curing shrinkage of a film is suppressed in a case of photocuring. Accordingly, the decrease of adhesiveness accompanied by curing shrinkage was suppressed. In a case where the curing shrinkage of the film in a case of photocuring is remarkable, adhesiveness between a film and a base material tends to decrease.

With respect to the water dispersion of the present disclosure, a resin emulsion in an ink composition for ink jet disclosed in JP2013-199602A and an aqueous emulsion disclosed in JP2000-136211A both do not have a three-dimensional crosslinked structure and are not gel particles.

This microgel in the colored photosensitive composition disclosed in JP2011-213114A does not have a polymerizable group. This microgel does not have Unit (1).

Accordingly, it is considered that a cured film formed by techniques of any documents also have deteriorated adhesiveness to a base material compared with the cured film formed by using the water dispersion of the present disclosure.

According to the water dispersion of the present disclosure, it is possible to form a film having excellent hardness (for example, pencil hardness).

It is considered that the reason is because, in the water dispersion of the present disclosure, as described above, the gel particles have a polymerizable group and include a photopolymerization initiator, the curing sensitivity is enhanced.

Since the water dispersion of the present disclosure is excellent in curing sensitivity, it is possible to form a film having excellent fixing properties to a base material and also having excellent water resistance and excellent solvent resistance with the water dispersion of the present disclosure.

Here, the “fixing properties of the film” are properties evaluated by an exposure amount until the film becomes sticky in a case where a film formed in a base material is exposed.

However, redispersibility is required to the water dispersion of the particles.

Here, the expression “redispersibility” refers to properties in which an aqueous solution (for example, water, an aqueous solution, or a water dispersion) is supplied to a solidified matter formed by evaporating water in a water dispersion, and particles in the solidified matter are dispersed again in the aqueous solution. Examples of the solidified matter include a solidified matter of a water dispersion formed on a coating head or an ink jet head.

The water dispersion of the present disclosure has excellent redispersibility as described above. It is considered that this is because, the particles have a three-dimensional crosslinked structure (that is, the particles are gel particles), structures of the respective particles become firm, and as a result, aggregation or coalescence of particles with each other are suppressed.

Therefore, even in a case where water in the water dispersion evaporated so as to form a solidified matter, water-based liquid (for example, water, a water dispersion, aqueous solution) is supplied to a solidified matter such that particles in the solidified matter are easily redispersed in a water-based liquid.

A hydrophilic group included in gel particles obviously contributes to the dispersibility and redispersibility of the gel particles.

In the water dispersion of the present disclosure, as described above, aggregation between particles with each other (gel particles with each other) is suppressed, and thus the water dispersion of the present disclosure is excellent in preservation stability.

The fact that the gel particles include a photopolymerization initiator has an advantage in that a photopolymerization initiator (for example, a photopolymerization initiator (for example, an acylphosphine oxide compound) of which solubility to water is 1.0 mass % or less at 25° C.) having low solubility to water can be easily used as a photopolymerization initiator.

In a case where gel particles include a photopolymerization initiator, there is an advantage in that a photopolymerization initiator to be used can be selected in a wider range.

Examples of the photopolymerization initiator having low solubility to water include an acylphosphine oxide compound (for example, a monoacylphosphine oxide compound and a bisacylphosphine oxide compound, a bisacylphosphine oxide compound is preferable. the same is applied below).

The acylphosphine oxide compound is a photopolymerization initiator having particularly excellent curing sensitivity to irradiation with active energy rays. However, since an acylphosphine oxide compound has low solubility to water, there was a problem in that an acylphosphine oxide compound is hardly contained in an aqueous composition (for example, even in a case where an acylphosphine oxide compound is contained, a large amount thereof cannot be contained) in the related art.

In the water dispersion of the present disclosure, in a case where the gel particles include a photopolymerization initiator, an acylphosphine oxide compound of which sensitivity to light is excellent but solubility to water is low and a photopolymerization initiator such as a carbonyl compound and an acylphosphine oxide compound can be selected.

In a case where the photopolymerization initiator is an acylphosphine oxide compound, sensitivity to light, particularly, sensitivity to LED light is enhanced.

The wavelength of the LED light is preferably 355 nm, 365 nm, 385 nm, 395 nm, or 405 nm.

The gel particles can include a component other than the photopolymerization initiator (such as a polymerizable monomer and a sensitizer).

In the water dispersion of the present disclosure, a substance having low solubility to water is caused to be included in the gel particles such that the substance having low solubility to water can be caused to be contained in the water dispersion liquid which is an aqueous composition. This is one of advantages of the water dispersion of the present disclosure.

<Inclusion>

In the present specification, the expression “a photopolymerization initiator is included in gel particles” means that a photopolymerization initiator is included inside the gel particles. Here, the expression “inside the gel particles” means cavities in a three-dimensional crosslinked structure.

In the water dispersion liquid of the present disclosure, in view of curing sensitivity of the film, an inclusion ratio (mass %) of the photopolymerization initiator is preferably 10 mass % or greater, more preferably 50 mass % or greater, even more preferably 70 mass % or greater, even more preferably 80 mass % or greater, even more preferably 90 mass % or greater, even more preferably 95 mass % or greater, even more preferably 97 mass % or greater, and particularly preferably 99 mass % or greater, in view of curing sensitivity of the film.

In a case where two or more photopolymerization initiators are contained in the water dispersion liquid, an inclusion ratio of at least one photopolymerization initiator is preferably in the above range.

Here, the inclusion ratio (mass %) of the photopolymerization initiator means an amount of the photopolymerization initiator included in the gel particles with respect to the total amount of the photopolymerization initiator in the water dispersion and refers to a value obtained as follows.

—Method of Measuring Inclusion Ratio (Mass %) of Photopolymerization Initiator—

The following operations are performed in the condition of the liquid temperature of 25° C.

In a case where a water dispersion is not contained in a pigment, the following operations are performed using this water dispersion without change. In a case where a water dispersion contains a pigment, a pigment is removed from the water dispersion by centrifugation, and the following operations are performed on the water dispersion from which the pigment is removed.

First, two samples (hereinafter, referred to as “Sample 1” and “Sample 2”) in the same amount are collected from the water dispersion which was a measurement target of an inclusion ratio (mass %) of the photopolymerization initiator.

With respect to Sample 1, 100 times by mass of tetrahydrofuran (THF) is mixed with a total solid content of Sample 1 so as to prepare a diluent. Centrifugation is performed in the condition of 40 minutes on the obtained diluent, at 80,000 rpm (round per minute; The same is applied to the followings). A supernatant (hereinafter, referred to as “Supernatant 1”) generated by centrifugation is collected. It is considered that all of the photopolymerization initiator included in Sample 1 is extracted to Supernatant 1 according to this operation. The mass of the photopolymerization initiator included in Supernatant 1 collected is measured by liquid chromatography (for example, a liquid chromatography device manufactured by Waters Corporation). The mass of the obtained photopolymerization initiator is called a “total amount of a photopolymerization initiator”.

Centrifugation in the same condition of the centrifugation performed by the diluent was performed on Sample 2. A supernatant (hereinafter, referred to as “Supernatant 2”) generated by centrifugation is collected. According to this operation, it is considered that a photopolymerization initiator that is not included in (that is, that is free from) the gel particles is extracted to Supernatant 2 in Sample 2. The mass of the photopolymerization initiator included in Supernatant 2 collected is measured by liquid chromatography (for example, a liquid chromatography device manufactured by Shimadzu Corporation). A mass of the obtained photopolymerization initiator is a “free amount of the photopolymerization initiator”.

An inclusion ratio (mass %) of the photopolymerization initiator is obtained by the following equation based on the total amount of the photopolymerization initiator and the free amount of the photopolymerization initiator. Inclusion ratio (mass %) of photopolymerization initiator=((total amount of photopolymerization initiator−free amount of photopolymerization initiator)/total amount of photopolymerization initiator)×100

In a case where the water dispersion includes two or more photopolymerization initiators, an entire inclusion ratio of two or more of the photopolymerization initiators may be obtained by using a total amount of the two or more photopolymerization initiators is set as a “total amount of the photopolymerization initiator” and using a sum of free amounts of the two or more photopolymerization initiators as a “free amount of the photopolymerization initiator”, and an inclusion ratio of any one of the photopolymerization initiators may be obtained by using an amount of any one photopolymerization initiator as a “total amount of the photopolymerization initiator” and using a free amount of one of the photopolymerization initiators as a “free amount of the photopolymerization initiator”.

In the water dispersion, whether components other than the photopolymerization initiator are included in the gel particles can be confirmed in the same manner as the method of examining whether the photopolymerization initiator is included.

However, with respect to the compound having a molecular weight of 1,000 or greater, masses of the compounds included in Supernatants 1 and 2 are measured by gel permeation chromatography (GPC), so as to obtain inclusion ratios (mass %) of the compound as a “total amount of the compound” and a “free amount of the compound”.

<Three-Dimensional Crosslinked Structure>

In the present disclosure, the “three-dimensional crosslinked structure” refers to a three-dimensional mesh structure formed by crosslinking. In the water dispersion according to the present disclosure, the gel particles are formed by forming a three-dimensional crosslinked structure in the particles.

That is, in the specification, the expression “the particles have a three-dimensional crosslinked structure” has the same meaning as the expression “the particles are the gel particles”.

The content of the three-dimensional crosslinked structure in the gel particles is preferably 10 mass % to 98 mass %, more preferably 20 mass % to 95 mass %, even more preferably 30 mass % to 90 mass %, even more preferably 30 mass % to 80 mass %, and particularly preferably 30 mass % to 70 mass % with respect to a total solid content of the gel particles.

Whether the water dispersion of the present disclosure includes gel particles having a three-dimensional crosslinked structure is checked as follows. The following operations are performed in the temperature condition of 25° C. In a case where the water dispersion is not contained in the pigment, the following operations are performed by using this water dispersion without change, and in a case where the water dispersion is contained in the pigment, a pigment was removed from the water dispersion by centrifugation and the following operations are performed on the water dispersion from which the pigment is removed.

Samples are gathered from the water dispersion. With respect to the gathered samples, 100 times by mass of tetrahydrofuran (THF) is added and mixed with respect to the total solid content of the sample so as to prepare a diluent. With respect to the obtained diluent, centrifugation is performed under the conditions of 80,000 rpm and 40 minutes. After the centrifugation, whether there are residues is visually checked. In a case where there are residues, the residues are re-dispersed with water, a redispersion liquid is prepared, and a particle size distribution of the redispersion liquid is measured by a light scattering method by using a wet-type particle size distribution determination device (LA-910, manufactured by Horiba Ltd.).

A case where particle size distribution can be checked by the operation described above is determined that the water dispersion includes gel particles having a three-dimensional crosslinked structure.

The three-dimensional crosslinked structure is not particularly limited, as long as the three-dimensional crosslinked structure includes a structural unit represented by Formula (1) and a urea bond (—NHC(═O)NH— bond). However, the three-dimensional crosslinked structure preferably includes a structure (that is, a structure obtained by reacting an isocyanate group-containing polymer and water) of a reaction product between an isocyanate group-containing polymer including a structural unit represented by Formula (1) and an isocyanate group (that is, an —N═C═O group) and water.

That is, an isocyanate group-containing polymer described herein is one of raw materials of the three-dimensional crosslinked structures. A preferable aspect of the isocyanate group-containing polymer is described below.

In the present specification, gel particles having a polymerizable group mean gel particles having at least one of a polymerizable group included in a three-dimensional crosslinked structure or a polymerizable group that is not included in a three-dimensional crosslinked structure.

That is, in the gel particles, the polymerizable group may exist as a portion of a three-dimensional crosslinked structure and may exist as a portion other than a three-dimensional crosslinked structure.

Here, the expression “a polymerizable group exists as a portion other than a three-dimensional crosslinked structure” means that a monomer (hereinafter, also referred to as a “polymerizable monomer”) having a polymerizable group is included in gel particles, independently from a three-dimensional crosslinked structure.

In any cases, it is preferable that the polymerizable group exists in surface portions (contact portion with water) of the gel particles.

The fact that “gel particles have a polymerizable group” can be checked, for example, by Fourier transform infrared spectroscopy (FT-IR) analysis.

Specific examples of the polymerizable monomer are provided below.

The polymerizable group is preferably a group including an ethylenic double bond and more preferably a group including at least one of a vinyl group or a 1-methylvinyl group.

In view of adhesiveness to a film, hardness of a film, and fixing properties (that is, reactivity in a case of photocuring), the polymerizable group is particularly preferably a (meth)acryloyl group.

According to the present disclosure, the gel particles having a hydrophilic group mean gel particles having at least one of a hydrophilic group included in a three-dimensional crosslinked structure or a hydrophilic group not included in a three-dimensional crosslinked structure.

That is, in the gel particles, a hydrophilic group may exist as a portion of a three-dimensional crosslinked structure and may exist as a portion other than the three-dimensional crosslinked structure.

Here, the expression “a hydrophilic group exists as a portion other than the three-dimensional crosslinked structure” means that a compound having a hydrophilic group is included in the gel particles, independently from a three-dimensional crosslinked structure.

In any cases, a hydrophilic group preferably exists on surface portions (contact portions with water) to gel particles.

In view of dispersibility of the gel particles and preservation stability of the water dispersion, the hydrophilic group included in the gel particles is preferably a carboxyl group, a salt of the carboxyl group, a sulfo group, a salt of the sulfo group, a sulfate group, a salt of the sulfate group, a phosphonic acid group, a salt of the phosphonic acid group, a phosphoric acid group, a salt of the phosphoric acid group, an ammonium salt group, a betaine group, or an alkyleneoxy group.

The gel particles may have only one kind of hydrophilic groups or may have two or more kinds thereof.

The above salt of the carboxyl group, the above salt of the sulfo group, the above salt of the sulfate group, the above salt of the phosphonic acid group, and the above salt of the phosphoric acid group may be salts formed by neutralization in the course of the producing of the gel particles.

Each of the above salt of the carboxyl group, the above salt of the sulfo group, the above salt of the sulfate group, the above salt of the phosphonic acid group, and the above salt of the phosphoric acid group is preferably alkali metal salts (for example, sodium salt and potassium salt).

In view of dispersibility of gel particles and preservation stability of a water dispersion, the hydrophilic group included in the gel particles is particularly preferably at least one group selected from the group consisting of a salt of the carboxyl group, a salt of the sulfo group, a salt of the sulfate group, and an alkyleneoxy group.

In the water dispersion of the present disclosure, the volume average particle diameter of the gel particles is preferably 0.05 μm to 0.60 μm.

In a case where the volume average particle diameter of the gel particles is 0.05 μm or greater, the gel particles can be easily produced, preservation stability of the water dispersion is enhanced.

The volume average particle diameter of the gel particles is more preferably 0.10 μm or greater.

Meanwhile, in a case where the volume average particle diameter of the gel particles is 0.60 μm or less, redispersibility of the water dispersion, jettability, and preservation stability are enhanced.

Since redispersibility of the water dispersion is enhanced, the volume average particle diameter of the gel particles is more preferably 0.50 μm or less, even more preferably 0.40 μm or less, and particularly preferably 0.30 μm or less.

In the present specification, the volume average particle diameter of the gel particles refers to a value measured by a light scattering method.

The measuring of the volume average particle diameter of gel particles by a light scattering method is performed by using, for example, LA-910 (manufactured by Horiba Ltd.).

The water dispersion of the present disclosure can be suitably used as a liquid for forming a film (for example, an image) on a base material (for example, a recording medium).

Examples of the liquid include an ink composition (for example, an ink composition for ink jet recording) for forming an image on a base material as a recording medium and a coating solution for forming a coated film on a base material.

Particularly, the water dispersion of the present disclosure is preferably a water dispersion (that is, the water dispersion of the present disclosure is an ink composition for ink jet recording) used in ink jet recording.

The ink composition (preferably ink composition for ink jet recording) which is one of uses of the water dispersion of the present disclosure may be an ink composition containing a colorant or a transparent ink composition (also referred to as “clear ink” and the like) not containing a colorant.

The same is applied to a coating liquid which is another use of the water dispersion of the present disclosure.

The base material for forming a film is not particularly limited, and well-known base materials can be used.

Examples of the base material include paper, paper obtained by laminating plastic (for example, polyethylene, polypropylene, or polystyrene), a metal plate (for example, a plate of metal such as aluminum, zinc, or copper), a plastic film (for example, a film of a polyvinyl chloride (PVC) resin, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate (PET), polyethylene (PE), polystyrene (PS), polypropylene (PP), polycarbonate (PC), polyvinyl acetal, and an acrylic resin), paper obtained by laminating or vapor-depositing the above metal, and a plastic film obtained by laminating or vapor-depositing the above metal.

Since the water dispersion of the present disclosure can form a film having excellent adhesiveness in a base material, the water dispersion is suitable and particularly suitable for the use of forming a film on a nonabsorbable base material.

The nonabsorbable base material is preferably a plastic base material such as a PVC base material, a PS base material, a PC base material, a PET base material, a glycol-modified PET base material, a PE base material, a PP base material, and an acrylic resin base material.

Hereinafter, each of the components of the water dispersion of the present disclosure is described.

<Gel Particles>

The water dispersion of the present disclosure includes gel particles dispersed in water.

The gel particles have a three-dimensional crosslinked structure including a structural unit represented by Formula (1) and a urea bond, having a hydrophilic group and a polymerizable group, and including a photopolymerization initiator.

Hereinafter, component elements in a three-dimensional crosslinked structure are described.

(Structural Unit Represented by Formula (1))

The three-dimensional crosslinked structure includes a structural unit (Unit (1)) represented by Formula (1). Accordingly, a three-dimensional crosslinked structure becomes firm.

A preferable aspect of the three-dimensional crosslinked structure is an aspect having a main chain including Unit (1).

R¹ in Formula (1) represents a hydrogen atom or an alkyl group.

X¹ in Formula (1) represents a hydrogen atom, a halogen atom, a hydroxyl group, an alkyl group, a cyano group, a lactam group, a —C(═O)X²R² group, an —OC(═O)R³ group, or an aryl group.

X² represents an oxygen atom or an —N(R^(X2))— group. R^(X2) represents a hydrocarbon group that may contain a hetero atom or a hydrogen atom.

R² represents a hydrocarbon group that may contain a hetero atom or a hydrogen atom. Here, in a case in which X² is an oxygen atom, R² is not a hydrogen atom. R² and R^(X2) may be bonded to each other to form a ring.

R³ represents a hydrocarbon group that may contain a hetero atom.

R² represents a hydrocarbon group that may contain a hetero atom or a hydrogen atom. Here, in a case where X² is an oxygen atom, R² does not have to be a hydrogen atom. R² and R^(X2) are bonded to each other to form a ring.

R³ represents a hydrocarbon group that may contain a hetero atom.

Since adhesiveness and hardness of a cured film are enhanced, X¹ is particularly preferably a —C(═O)X²R² group.

Unit (1) in a case where X¹ is a —C(═O)X²R² group is a structural unit (referred to as “Unit (1A)”) represented by Formula (1A).

In Formula (1A), R¹, R², and X² are the same respectively as R¹, R², and X² in Formula (1).

Hereinafter, Formula (1) is described.

R¹ represents a hydrogen atom or an alkyl group.

R¹ is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms (more preferably 1 to 6 carbon atoms and even more preferably 1 to 3 carbon atoms), more preferably a hydrogen atom, a methyl group, or an ethyl group, and particularly preferably a hydrogen atom or a methyl group.

X¹ represents a hydrogen atom, a halogen atom, a hydroxyl group, an alkyl group, a cyano group, a lactam group, a —C(═O)X²R² group, an —OC(═O)R³ group, or an aryl group.

A halogen atom represented by X¹ is preferably a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, more preferably a fluorine atom, a chlorine atom, or a bromine atom, and particularly preferably a fluorine atom or a chlorine atom.

The alkyl group represented by X¹ is preferably an alkyl group having 1 to 10 carbon atoms (more preferably having 1 to 6 carbon atoms and even more preferably having 1 to 3 carbon atoms), more preferably a methyl group or an ethyl group, and particularly preferably a methyl group.

The lactam group represented by X¹ is preferably a lactam group having a 4-membered ring to 10-membered ring structure, preferably a lactam group having a 5-membered ring to 10-membered ring structure, more preferably a lactam group having a 5-membered ring to 9-membered ring structure, even more preferably a lactam group having a 5-membered ring to 8-membered ring structure, and particularly preferably a lactam group having a 5-membered ring structure or 7-membered ring structure.

In a —C(═O)X²R² group represented by X¹, X² represents an oxygen atom or an —N(R^(X2))— group. R^(X2) represents a hydrocarbon group that may contain a hetero atom or a hydrogen atom.

A hydrocarbon group including a hetero atom in the expression “hydrocarbon group that may contain a hetero atom” in Formula (1) means a group in a structure in which a portion of carbon atoms in a group consisting of a carbon atom and a hydrogen atom is substituted with a hetero atom.

The hetero atom is preferably an oxygen atom, a nitrogen atom, or a sulfur atom and more preferably an oxygen atom or a nitrogen atom.

In the present specification, meanings and preferable ranges of a “hydrocarbon group that may contain a hetero atom” in formulae (for example, Formulae (2) and (3)) other than Formula (1) are the same as the meaning and the preferable range of a “hydrocarbon group that may contain a hetero atom” in Formula (1).

The number of carbon atoms in the hydrocarbon group that may contain a hetero atom is preferably 1 to 30, more preferably 1 to 25, and particularly preferably 1 to 18.

Specific examples of the hydrocarbon group that may contain a hetero atom include an alkyl group having 1 to 30 carbon atoms, an alkoxyalkyl group having 2 to 30 carbon atoms, a polyalkoxyalkyl group having 3 to 30 carbon atoms, an aryloxyalkyl group having 7 to 30 carbon atoms, an aminoalkyl group having 1 to 30 carbon atoms, a monoalkylaminoalkyl group having 2 to 30 carbon atoms, and a dialkylaminoalkyl group having 3 to 30 carbon atoms.

R^(X2) is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms (preferably 1 to 6 carbon atoms and more preferably 1 to 3 carbon atoms) and more preferably a hydrogen atom or a methyl group.

In the —C(═O)X²R² group, X² is preferably an oxygen atom, a —NH— group, or a —N(CH₃)— group and more preferably an oxygen atom or a —N(CH₃)— group.

In the —C(═O)X²R² group, R² is preferably an alkyl group having 1 to 30 carbon atoms, an alkoxyalkyl group having 2 to 30 carbon atoms, a polyalkoxyalkyl group having 3 to 30 carbon atoms, an aryloxyalkyl group having 7 to 30 carbon atoms, an aminoalkyl group having 1 to 30 carbon atoms, a monoalkylaminoalkyl group having 2 to 30 carbon atoms, or a dialkylaminoalkyl group having 3 to 30 carbon atoms.

An alkyl group having 1 to 30 carbon atoms, which is a preferable aspect of R² may be a linear alkyl group, a branched alkyl group, a cyclic alkyl group. However, in view of the enhancement of the hardness and adhesiveness of the cured film, an alkyl group having 1 to 30 carbon atoms is particularly preferably a cyclic alkyl group having 6 to 30 carbon atoms (preferably 6 to 25 carbon atoms, more preferably 6 to 18 carbon atoms, and even more preferably 6 to 12 carbon atoms).

In view of enhancement of the hardness and the adhesiveness of the cured film, R² is particularly preferably a cyclic alkyl group having 6 to 30 carbon atoms (preferably having 6 to 25 carbon atoms, more preferably having 6 to 18 carbon atoms, and even more preferably 6 to 12 carbon atoms) or an aryloxyalkyl group having 7 to 30 carbon atoms (preferably having 7 to 25 carbon atoms, more preferably 7 to 18 carbon atoms, and even more preferably 7 to 12 carbon atoms).

In an —OC(═O)R³ group represented by X¹, R³ is more preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 6 carbon atoms, and particularly preferably an alkyl group having 1 to 3 carbon atoms.

Examples of the aryl group represented by X¹ include a phenyl group and a naphthyl group, and a phenyl group is preferable.

The aryl group may be an unsubstituted aryl group or a substituted aryl group.

Examples of a substituent in the substituted aryl group include a halogen atom (preferably a fluorine atom, a chlorine atom, or a bromine atom; more preferably a fluorine atom or a chlorine atom), an alkyl group having 1 to 3 carbon atoms, and an alkoxy group having 1 to 3 carbon atoms. The substituent is preferably a fluorine atom, a chlorine atom, a methyl group, or a methoxy group. The number of substituents in a case where an aryl group has a substituent is preferably 1 to 5, more preferably 1 to 3, even more preferably 1 or 2, and particularly preferably 1.

A preferable combination of groups in Formula (1) include a combination in which:

R¹ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms (more preferably 1 to 6 carbon atoms and more preferably 1 to 3 carbon atoms),

X¹ is a hydrogen atom, a halogen atom, a hydroxyl group, an alkyl group having 1 to 10 carbon atoms (more preferably 1 to 6 carbon atoms and more preferably 1 to 3 carbon atoms), a cyano group, a lactam group (preferably lactam group having a 5-membered ring to 10-membered ring structure), a —C(═O)X²R² group, an —OC(═O)R³ group, and or an aryl group,

X² is an oxygen atom or an —N(R^(X2))— group,

R^(X2) is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms (more preferably having 1 to 6 carbon atoms and even more preferably 1 to 3 carbon atoms),

R² is a hydrogen atom, an alkyl group having 1 to 30 carbon atoms, an alkoxyalkyl group having 2 to 30 carbon atoms, a polyalkoxyalkyl group having 3 to 30 carbon atoms, an aryloxyalkyl group having 7 to 30 carbon atoms, an aminoalkyl group having 1 to 30 carbon atoms, a monoalkylaminoalkyl group having 2 to 30 carbon atoms, or a dialkylaminoalkyl group having 3 to 30 carbon atoms, and

R³ is an alkyl group having 1 to 6 carbon atoms.

In X¹ of Formula (1), specific examples of the —C(═O)X²R² group (* indicates a bonding position) are as follows. Here, the present invention is not limited to these specific example.

In X¹ of Formula (1), specific examples other than the —C(═O)X²R² group (* indicates a bonding position) are as follows. Here, the present invention is not limited to these specific examples.

A structural unit (Unit (1)) represented by Formula (1) included in the three-dimensional crosslinked structure may be used singly or two or more kinds thereof may be used in combination.

In view of adhesiveness and hardness of the cured film, the content of Unit (1) (total content in a case where two or more kinds are used. The same is applied in the followings) in the three-dimensional crosslinked structure is preferably 50 mass % or greater, more preferably 60 mass % or greater, even more preferably 70 mass % or greater, and particularly preferably 80 mass % or greater with respect to a total amount of the three-dimensional crosslinked structure.

The upper limit of the content of Unit (1) is not particularly limited. The content of Unit (1) may be 100 mass % or may be less than 100 mass % (preferably 99 mass % or less, more preferably 95 mass % or less, and even more preferably 90 mass % or less) with respect to the total amount of the three-dimensional crosslinked structure.

(Urea Bond)

The three-dimensional crosslinked structure includes a urea bond. Accordingly, the three-dimensional crosslinked structure becomes firm.

Since adhesiveness and hardness are enhanced, the three-dimensional crosslinked structure preferably includes at least one of a structural unit including a urea bond or a group including a urea bond.

The structural unit including an urea bond is preferably a structural unit represented by Formula (2).

A group including an urea bond is preferably a group represented by Formula (3).

The three-dimensional crosslinked structure may include both a structural unit represented by Formula (2) and a structural unit represented by Formula (3).

(Structural Unit Represented by Formula (2))

As described below, a structural unit (hereinafter, also referred to as “Unit (2)”) represented by Formula (2) may include a urea bond in a portion of a side chain.

A preferable aspect of a three-dimensional crosslinked structure is an aspect of having a main chain including Unit (1) and Unit (2).

R²¹ in Formula (2) represents a hydrogen atom or an alkyl group.

L²¹ in Formula (2) represents a divalent hydrocarbon group that may contain a hetero atom.

X²¹ in Formula (2) represents an oxygen atom or a —C(═O)X²²L²²O— group.

X²² represents an oxygen atom or a —N(R^(x22))— group. R^(X22) represents a hydrocarbon group that may contain a hetero atom.

L²² represents a divalent hydrocarbon group that may contain a hetero atom.

In Formula (2), p represents 0 or 1.

In Formula (2), * represents a bonding position.

R²¹ in Formula (2) is the same as R¹ in Formula (1), and preferable ranges thereof are also the same.

In view of hardness of the cured film, p in Formula (2) is preferably 1.

Since adhesiveness and hardness of the cured film are enhanced, X²¹ in Formula (2) is preferably a —C(═O)X²²L²²O— group.

Unit (2) in a case where X²¹ is a —C(═O)X²²L²²O— group is a structural unit (also referred to as “Unit (2A)”) represented by Formula (2A).

In Formula (2A), R²¹, X²², L²², p, and L²¹ are the same respectively as R²¹, X²², L²², p, and L²¹ in Formula (2).

Hereinafter, Formula (2) is further described.

L²¹ in Formula (2) represents a divalent hydrocarbon group that may contain a hetero atom.

Here, a divalent hydrocarbon group including a hetero atom in the divalent hydrocarbon group that may contain a hetero atom means a group in a structure in which at least one carbon atom of divalent hydrocarbon groups is substituted with a hetero atom.

The hetero atom is preferably a nitrogen atom, an oxygen atom, or a sulfur atom.

The divalent hydrocarbon group before being substituted with a hetero atom may be any one of an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group, is preferably an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, more preferably an aliphatic hydrocarbon group, and particularly preferably an alkylene group.

The number of carbon atoms in the divalent hydrocarbon group that may contain a hetero atom is preferably 1 to 30, more preferably 3 to 30, and particularly preferably 6 to 30.

X²¹ in Formula (2) represents an oxygen atom or a —C(═O)X²²L²²O— group.

X²² represents an oxygen atom or a —N(R^(X22))— group. R^(X22) represents a hydrocarbon group that may contain a hetero atom.

L²² represents a divalent hydrocarbon group that may contain a hetero atom.

A hydrocarbon group that may contain a hetero atom, which is represented by R^(X22) is the same as the hydrocarbon group that may contain a hetero atom in Formula (1).

R^(X22) is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms (preferably having 1 to 6 carbon atoms and more preferably 1 to 3 carbon atoms) and more preferably a hydrogen atom or a methyl group.

L²¹ and L²² each independently and preferably represent an alkylene group having 1 to 30 carbon atoms, an arylene group having 6 to 30 carbon atoms, an alkylene arylene group having 7 to 30 carbon atoms, an alkylene arylene alkylene group having 8 to 30 carbon atoms, an alkyleneoxyalkylene group having 2 to 30 carbon atoms, or an alkylene polyoxyalkylene group having 3 to 30 carbon atoms.

Since hardness and adhesiveness of the cured film are enhanced, L²¹ is preferably

a cyclicalkylene group having 6 to 30 carbon atoms (preferably having 6 to 20 carbon atoms and more preferably 6 to 13 carbon atoms),

an arylene group having 6 to 30 carbon atoms (preferably having 6 to 20 carbon atoms and more preferably 6 to 13 carbon atoms),

an alkylene arylene group having 7 to 30 carbon atoms (preferably having 7 to 20 carbon atoms and more preferably 7 to 13 carbon atoms),

an alkylene arylene alkylene group having 8 to 30 carbon atoms (preferably having 8 to 20 carbon atoms and more preferably 8 to 13 carbon atoms),

an alkyleneoxyalkylene group having 2 to 30 carbon atoms (preferably having 7 to 20 carbon atoms and more preferably 7 to 13 carbon atoms), or

an alkylene polyoxyalkylene group having 3 to 30 carbon atoms. Among these,

a cyclicalkylene group having 1 to 30 carbon atoms (preferably having 6 to 20 carbon atoms and more preferably 6 to 13) is preferable.

In view of producing easiness, L²² is more preferably a chain alkylene group having 1 to 30 carbon atoms (preferably 1 to 10 carbon atoms and more preferably 1 to 6 carbon atoms), an alkyleneoxyalkylene group having 2 to 30 carbon atoms (preferably 2 to 10 carbon atoms and more preferably 2 to 6 carbon atoms), or an alkylene polyoxyalkylene group having 3 to 30 carbon atoms (preferably 3 to 10 carbon atoms and more preferably 3 to 6 carbon atoms), and even more preferably a chain alkylene group having 1 to 30 carbon atoms (preferably 1 to 10 carbon atoms and more preferably 1 to 6 carbon atoms).

In view of adhesiveness, L²² is particularly preferably an alkylene group having 1 to 3 carbon atoms (more preferably 1 or 2 carbon atoms).

A preferable combination of respective groups in Formula (2) is a combination in which:

R²¹ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms,

L²¹ is an alkylene group having 1 to 30 carbon atoms, an arylene group having 6 to 30 carbon atoms, an alkylene arylene group having 7 to 30 carbon atoms, an alkylene arylene alkylene group having 8 to 30 carbon atoms, an alkyleneoxyalkylene group having 2 to 30 carbon atoms, or an alkylene polyoxyalkylene group having 3 to 30 carbon atoms,

X²¹ is an oxygen atom or a —C(═O)X²²L²²O— group,

X²² is an oxygen atom or a —N(R^(x22))— group,

R^(x22) is an alkyl group having 1 to 6 carbon atoms, and

L²² is an alkylene group having 1 to 30 carbon atoms, an arylene group having 6 to 30 carbon atoms, an alkylene arylene group having 7 to 30 carbon atoms, an alkylene arylene alkylene group having 8 to 30 carbon atoms, an alkyleneoxyalkylene group having 2 to 30 carbon atoms, or an alkylene polyoxyalkylene group having 3 to 30 carbon atoms.

Specific examples of L²¹ and L²² are provided below. Here, the present invention is not limited to these specific examples.

q1 and q2 each independently represent an integer selected from 1 to 100.

In the specific example, * and ** all indicate bonding positions.

In examples having both * and **, ** indicates a bonding position that is bonded to a urea bond side in Formula (2).

In the above specific example, any groups may be used as L²¹. However, Groups (L-8) to (L-17) are preferable in view of hardness of a cured film, and Groups (L-12) to (L-17) are more preferable in view of hardness and adhesiveness of the cured film.

In the above specific examples, any groups may be used as L²². However, in view of producing easiness, Groups (L-1) to (L-7), (L-18), or (L-19) are preferable. In view of adhesiveness of a cured film, L²² is preferably Groups (L-1) to (L-7) and particularly preferably Group (L-1) or (L-2).

Subsequently, specific examples of Unit (2) are provided. Here, the present invention is not limited to these specific examples.

In the following specific examples, q1 and q2 each independently represent an integer selected from 1 to 100.

In a case where a three-dimensional crosslinked structure includes a structural unit (Unit (2)) represented by Formula (2), Unit (2) may be included singly or two or more kinds thereof may be included.

In a case where the three-dimensional crosslinked structure includes Unit (2), a content (total content in a case where two or more kinds are used) of Unit (2) in a three-dimensional crosslinked structure is preferably 1 mass % to 40 mass %, more preferably 3 mass % to 30 mass %, even more preferably 3 mass % to 20 mass %, and particularly preferably 5 mass % to 15 mass % with respect to a total amount of a three-dimensional crosslinked structure, in view of adhesiveness and hardness of the cured film.

In Formula (3), Z³¹ represents a (n+1)-valent organic group, and Z³² represents a (m+1)-valent organic group.

In Formula (3), n represents an integer of 1 to 4, and m represents an integer of 1 to 4.

In Formula (3), * represents a bonding position.

In Formula (3), n is preferably an integer of 1 to 3 and particularly preferably 2.

In Formula (3), m is preferably an integer of 1 to 3 and particularly preferably 2.

The (n+1)-valent organic group represented by Z³¹ is preferably a (n+1)-valent hydrocarbon group that may contain a hetero atom.

The meaning of the hydrocarbon group that may contain a hetero atom is as described above.

The number of carbon atoms in the (n+1)-valent organic group is preferably 2 to 30, more preferably 2 to 20, and particularly preferably 2 to 10.

Specific examples of the (n+1)-valent organic group represented by Z³¹ are provided below.

In the specific examples, * represents the same bonding position as * in Formula (3). *1 and *2 represent bonding positions that are bonded to oxygen atoms in Formula (3).

The (m+1)-valent organic group represented by Z³² is preferably a (m+1)-valent hydrocarbon group that may contain a hetero atom.

The meaning of the hydrocarbon group that may contain a hetero atom is as described above.

The number of carbon atoms in the (m+1)-valent organic group is preferably 2 to 100, more preferably 4 to 50, and particularly preferably 6 to 30.

Specific examples of the (m+1)-valent organic group represented by Z³² are provided below.

In the specific examples, * represents a bonding position, and L represents any one of Groups (L-5) to (L-17).

In a case where a three-dimensional crosslinked structure includes a group (Group (3)) represented by Formula (3), Group (3) may be included singly or two or more kinds thereof may be included.

In a case where a three-dimensional crosslinked structure includes Group (3), the content (total content in a case where two or more kinds are used) of Group (3) in the three-dimensional crosslinked structure is preferably 1 mass % to 40 mass %, more preferably 3 mass % to 30 mass %, even more preferably 3 mass % to 20 mass %, and particularly preferably 5 mass % to 15 mass % with respect to a total amount of a three-dimensional crosslinked structure, in view of adhesiveness and hardness of the cured film.

(Structural Unit Represented by Formula (G))

In a case where X¹ in Formula (1) is a —C(═O)X²R² group, the three-dimensional crosslinked structure preferably includes a structural unit (hereinafter, referred to as “Unit (G)”) represented by Formula (G). Accordingly, adhesiveness and hardness of a cured film are enhanced.

An aspect of including Unit (G) is preferably an aspect in which graft polymerization is performed on a polymer including Unit (1) in a side chain portion of Unit (G).

R^(G1) in Formula (G) represents a hydrogen atom or an alkyl group.

Z^(G1) in Formula (G) represents a divalent organic group.

*G in Formula (G) represents a bonding position of being bonded to a structural unit represented by Formula (1).

R^(G1) in Formula (G) is the same as R¹ in Formula (1), and preferable ranges thereof are also the same.

The divalent organic group represented by Z^(G1) is preferably a divalent hydrocarbon group that may contain a hetero atom.

The meaning of the hydrocarbon group that may contain a hetero atom is as described below.

The number of carbon atoms of the divalent organic group is preferably 1 to 30, more preferably 2 to 20, and particularly preferably 2 to 10.

A unit in which Unit (G) and Unit (1) (here, X¹ is a —C(═O)X²R² group) are bonded to each other is a structural unit (hereinafter, also referred to as “Unit (G1)”) represented by Formula (G1).

In Formula (G1), R^(G1) and Z^(G1) are the same respectively as R^(G1) and Z^(G1) in Formula (G).

In Formula (G1), R¹, R², and X² are the same respectively as R¹, R², and X² in Formula (1).

Specific examples of the divalent organic group represented by Z^(G1) are provided below. In the specific examples, *1 indicates a bonding position to an oxygen atom, and *2 indicates a bonding position to an carbon atom.

Unit (G1) can be formed, for example, by using a macromonomer “ARONIX (Registered trademark) AA-6” manufactured by Toagosei Co., Ltd.

In a case where the three-dimensional crosslinked structure includes Unit (G), Unit (G) may be included singly or two or more kinds thereof may be included.

In a case where the three-dimensional crosslinked structure includes Unit (G), a content (total content in a case where two or more kinds are used) of Unit (G) in the three-dimensional crosslinked structure is preferably 50 mass % or greater, more preferably 60 mass % or greater, even more preferably 70 mass % or greater, and particularly preferably 80 mass % or greater with respect to a total amount of the three-dimensional crosslinked structure, in view of adhesiveness and hardness of a cured film.

The upper limit of the content of Unit (G) is not particularly limited. The content of Unit (G) may be 100 mass % or may be less than 100 mass % (preferably 99 mass % or less, more preferably 95 mass % or less, and even more preferably 90 mass % or less) with respect to the total amount of the three-dimensional crosslinked structure.

(Structural Unit Represented by Formula (W))

The three-dimensional crosslinked structure preferably includes a structural unit (hereinafter, also referred to as “Unit (W)”) represented by Formula (W). Accordingly, preservation stability of the water dispersion is enhanced.

Unit (W) includes W¹ that is a hydrophilic group.

An aspect in which a three-dimensional crosslinked structure includes Unit (W) is one aspect in which a hydrophilic group exists as a portion of a three-dimensional crosslinked structure in gel particles.

R^(W1) in Formula (W) represents a hydrogen atom or an alkyl group.

W¹ in Formula (W) represents a monovalent group including at least one selected from the group consisting of a carboxyl group, a salt of the carboxyl group, a sulfo group, a salt of the sulfo group, a sulfate group, a salt of the sulfate group, a phosphonic acid group, a salt of the phosphonic acid group, a phosphoric acid group, a salt of the phosphoric acid group, an ammonium salt group, a betaine group, and an alkyleneoxy group.

R^(W1) in Formula (W) is the same as R¹ in Formula (1), and preferable ranges are also the same.

A “salt” in W¹ is preferably alkali metal salt, more preferably sodium salt or potassium salt, and particularly preferably sodium salt.

W¹ is preferably a carboxyl group, a salt of the carboxyl group, a —C(═O)NH—R^(W2)—SO₃H group, a salt of the —C(═O)NH—R^(W3)—SO₃H group, a —C(═O)NH—R^(W4)—OSO₃H group, a salt of the —C(═O)NH—R^(W5)—OSO₃H group, or a —C(═O)O—(R^(W6)O)_(nw)—R^(W7) group.

Here, R^(W2) to R^(W6) each independently represent an alkylene group having 1 to 10 carbon atoms, a R^(W7) group represents an alkyl group having 1 to 10 carbon atoms, and nw represents an integer of 1 to 200.

The number of carbon atoms in the alkylene group having 1 to 10 carbon atoms, which is represented by R^(W2) to R^(W5) is preferably 1 to 6.

The number of carbon atoms in the alkylene group having 1 to 10 carbon atoms, which is represented by R^(W6) is preferably 1 to 8, more preferably 2 to 4, and particularly preferably 2 or 3.

The number of carbon atoms in the alkyl group having 1 to 10 carbon atoms, which is represented by R^(W7) is preferably 1 to 8, even more preferably 1 or 2, and particularly preferably 1.

nw is more preferably an integer of 2 to 150 and particularly preferably an integer of 50 to 150.

In view of preservation stability, W¹ is preferably a salt of the carboxyl group, a salt of the —C(═O)NH—R^(W3)—SO₃H group, a salt of the —C(═O)NH—R^(W5)—OSO₃H group, or a —C(═O)O—(R^(W6)O)_(n)—R^(W7) group.

Unit (W) in an aspect in which W¹ is a “salt” (a salt of the carboxyl group, a salt of the sulfo group, a salt of the sulfate group, and the like) is a salt obtained by neutralization in the course of producing a water dispersion.

That is, in a stage in which a polymer (for example, the following isocyanate group-containing polymer) that becomes a raw materials of a three-dimensional crosslinked structure is synthesized, a group corresponding to W¹ may be a group which is not a salt (carboxyl group, a sulfo group, a sulfate group, and the like). Thereafter, a salt as W¹ may be formed by neutralization.

Examples of the monomer for forming Unit (W) include (meth)acrylic acid or a salt thereof; a sulfonic acid compound having a polymerizable group such as 2-acrylamido-2-methylpropanesulfonic acid (hereinafter, also referred to as “AMPS”), vinyl sulfonic acid, vinyl sulfate, and sulfopropyl acrylate, and a salt thereof; and polyalkylene glycol(meth)acrylate.

Polyalkylene glycol (meth)acrylate is preferably polyalkylene glycol mono(meth)acrylate, polyalkylene glycol di(meth)acrylate, or alkoxypolyalkylene glycol mono(meth)acrylate.

All of polyalkylene glycol (meth)acrylate is preferably a compound in which a repetition number of an alkyleneoxy group is 1 to 200 (more preferably 2 to 150 and more preferably 50 to 150).

The number of carbon atoms in an alkyleneoxy group in polyalkylene glycol (meth)acrylate is preferably 1 to 10, more preferably 1 to 8, more preferably 2 to 4, and particularly preferably 2 or 3 (that is, an alkyleneoxy group is an ethyleneoxy group or a propyleneoxy group).

The number of carbon atoms in the alkoxy group in alkoxypolyalkylene glycol mono(meth)acrylate is preferably 1 to 10, more preferably 1 to 8, more preferably 1 to 2, and particularly preferably 1 (that is, an alkoxy group is a methoxy group).

The polyalkylene glycol (meth)acrylate is particularly preferably methoxy polyethylene glycol methacrylate.

As polyalkylene glycol (meth)acrylate, a commercially available product can be used.

Examples of the commercially available product include a BLEMMER (Registered trademark) series manufactured by NOF Corporation.

In a case where the three-dimensional crosslinked structure includes Unit (W), Unit (W) may be included singly or two or more kinds thereof may be included.

In a case where the three-dimensional crosslinked structure includes Unit (W), the content (total content in a case where two or more kinds are used) of Unit (W) in the three-dimensional crosslinked structure is preferably 1 mass % to 40 mass %, more preferably 3 mass % to 30 mass %, even more preferably 3 mass % to 20 mass %, and particularly preferably 5 mass % to 15 mass % with respect to a total amount of the three-dimensional crosslinked structure.

The three-dimensional crosslinked structure may include other structural units in addition to the above.

Examples of the other structural unit include a structural unit having a polymerizable group. An aspect in which the three-dimensional crosslinked structure includes a structural unit having a polymerizable group is one of aspects in which a polymerizable group exists as a portion of the three-dimensional crosslinked structures in the gel particles.

The polymerizable group may be introduced in the course of forming a three-dimensional crosslinked structure or may be introduced after a three-dimensional crosslinked structure is formed.

Hereinafter, specific examples (Structures (S-1) to (S-44)) of the three-dimensional crosslinked structure are provided below, but the present invention is not limited to these specific examples.

In Structures (S-1) to (S-44), a number applied to the lower right of each of the structural units indicates a copolymerization mass ratio.

Here, a number applied to the lower right of each of ethyleneoxy groups (for example, “90” in Structure (S-43)) indicates a repetition number of an ethyleneoxy group, a number applied to the lower right of each of repeating units in a graft chain (for example, “60” in Structure (S-43)) indicates a repetition number of the repeating unit in the graft chain.

Structures (S-31), (S-32), (S-42), and (S-43) are specific examples of a three-dimensional crosslinked structure including Unit (G1), and “—X—” in these structures represents a divalent organic group.

“R—S—*” in Structure (S-7) to (S-9), (S-28) to (S-30), and (S-39) to (S-41) is a group described below and a specific example of Group (3).

(Isocyanate Group-Containing Polymer)

As described above, a method of forming a three-dimensional crosslinked structure including Unit (1) and a urea bond is not particularly limited. However, a method of forming a three-dimensional crosslinked structure by reaction between an isocyanate group-containing polymer including Unit (1) and an isocyanate group (an —N═C═O group; hereinafter, referred to as “—NCO”) and water is suitable.

In the reaction, an isocyanate group-containing polymer is one of raw materials in a three-dimensional crosslinked structure.

According to the reaction, a urea bond is formed by reaction among an isocyanate group in a specific molecule of the isocyanate group-containing polymer, an isocyanate group in one molecule different from an isocyanate group-containing polymer, and water. According to the forming of this urea bond, molecules of the isocyanate group-containing polymer are bonded to each other, and as a result, a three-dimensional crosslinked structure including Unit (1) and a urea bond is formed.

The fact that a urea bond is formed by reaction between an isocyanate group and water is formed is well-known in the art, and thus descriptions of specific mechanisms of the reaction are omitted in the present specification.

The isocyanate group-containing polymer includes Unit (1) (structural unit represented by Formula (1)) and an isocyanate group.

A preferable aspect of an isocyanate group-containing polymer is an aspect in which a urea bond (a —NHC(═O)NH— bond) in the above preferable aspect of the three-dimensional crosslinked structure is substituted with an isocyanate group (an —N═C═O group).

That is, preferable aspects (also including the preferable range of the content of Unit (1)) of Unit (1) in an isocyanate group-containing polymer are the same as the preferable aspect (also including the preferable range of the content of Unit (1)) of Unit (1) in the three-dimensional crosslinked structure.

The isocyanate group-containing polymer preferably includes at least one structural unit (hereinafter, referred to as “Unit (I-2)”) represented by Formula (I-2) or a group (hereinafter, referred to as “Group (I-3)”) represented by Formula (I-3).

In Formula (I-2), R²¹, X²¹, L²¹, and p are also the same as R²¹, X²¹, L²¹, and p in Formula (2), and the preferable ranges thereof are also the same.

In Formula (I-3), Z³¹, Z³², m, and n are the same respectively as Z³¹, Z³², m, and n in Formula (3), and the preferable ranges are also the same.

In the isocyanate group-containing polymer, the preferable range of the content of Unit (I-2) and the preferable range of the content of Group (I-3) are respectively the same as the preferable range of the content of Unit (2) and the preferable range of the content of Group (3) in the three-dimensional crosslinked structure.

A weight-average molecular weight (Mw) of the isocyanate group-containing polymer is not particularly limited, and is preferably 5,000 to 200,000, more preferably 8,000 to 100,000, even more preferably 10,000 to 50,000, and particularly preferably 15,000 to 40,000.

In a case where Mw is 5,000 or greater, a three-dimensional crosslinked structure is easily formed.

In a case where Mw is 200,000 or less, an isocyanate group-containing polymer is easily produced.

Specific examples of the isocyanate group-containing polymer include Isocyanate Group-Containing Polymers P-1 to P-44 in a structure in which a urea bond (a —NHC(═O)NH— bond) is substituted with an isocyanate group (an —N═C═O group) in Exemplary Structures (S-1) to (S-44) which are specific examples of the three-dimensional crosslinked structure. Descriptions of structures of Isocyanate Group-Containing Polymers P-1 to P-44 are omitted.

(Photopolymerization Initiator)

The gel particles include a photopolymerization initiator.

The inclusion is as described above.

For example, the water dispersion of the present disclosure may include only one kind of photopolymerization initiators or may include two or more kinds thereof. For example, the gel particles may include only one kind of photopolymerization initiators or may include two or more kinds thereof.

The photopolymerization initiator is a compound that absorbs active energy rays and generates radicals which are polymerization initiating species.

Examples of the active energy rays include γ rays, β rays, electron beams, ultraviolet rays, visible rays, and infrared rays.

As the photopolymerization initiator, the well-known compounds can be used. Examples of the preferable photopolymerization initiator include (A) a carbonyl compound such as aromatic ketones, (b) an acylphosphine oxide compound, (c) an aromatic onium salt compound, (d) organic peroxide, (e) a thio compound, (f) a hexaarylbiimidazole compound, (g) a ketoxime ester compound, (h) a borate compound, (i) an azinium compound, (j) a metallocene compound, (k) an active ester compound, (1) a compound having a carbon halogen bond, and (m) an alkylamine compound.

These photopolymerization initiators may use compounds of (a) to (m) singly or two or more kinds thereof in combination.

Preferable examples of (a) the carbonyl compound, (b) the acylphosphine oxide compound, and (e) the thio compound include compounds having a benzophenone skeleton or a thioxanthone skeleton disclosed in “RADIATION CURING IN POLYMER SCIENCE AND TECHNOLOGY”, J. P. FOUASSIER, J. F. RABEK (1993), pp. 77 to 117.

More preferable examples thereof include α-thiobenzophenone compounds disclosed in JP1972-6416B (JP-S47-6416B), a benzoin ether compound disclosed in JP1972-3981B (JP-S47-3981B), an α-substituted benzoin compound JP1972-22326B (JP-S47-22326B), a benzoin derivative disclosed in JP1972-23664B (JP-S47-23664B), aroylphosphonic acid ester disclosed in JP1982-30704B (JP-S57-30704B), dialkoxybenzophenone disclosed in JP1985-26483A (JP-S60-26483A), benzoin ethers disclosed in JP1985-26403B (JP-S60-26403B) and JP1987-81345A (JP-S62-81345A), α-aminobenzophenones disclosed in JP1989-34242B (JP-H01-34242B), U.S. Pat. No. 4,318,791A, and EP0284561A1, p-di(dimethylamino benzoyl) benzene disclosed in JP1990-211452A (JP-H02-211452A), thio-substituted aromatic ketone disclosed in JP1986-194062A (JP-S61-194062A), acyl phosphine sulfide disclosed in JP1990-9597A (JP-H02-9597A), acyl phosphine disclosed in JP1990-9596B (JP-H02-9596B), thioxanthones as disclosed in JP1988-61950B (JP-S63-61950B), and coumarin disclosed in JP1984-42864B (JP-S59-42864B).

Polymerization initiators disclosed in JP2008-105379A or JP2009-114290A are also preferable.

Among these photopolymerization initiators, (a) the carbonyl compound and (b) the acylphosphine oxide compound are more preferable. Specific examples thereof include bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (for example, IRGACURE (Registered trademark) 819: manufactured by BASF SE), 2-(dimethylamine)-1-(4-morpholinophenyl)-2-benzyl-1-butanone (for example, IRGACURE (Registered trademark) 369: manufactured by BASF SE), 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one (for example, IRGACURE (Registered trademark) 907: manufactured by BASF SE), 1-hydroxy-cyclohexyl-phenyl-ketone (for example, IRGACURE (Registered trademark) 184: manufactured by BASF SE), and 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (for example, DAROCUR (Registered trademark) TPO and LUCIRIN (Registered trademark) TPO: all manufactured by BASF SE).

Among these, in view of sensitivity enhancement and suitability to LED light, (b) the acylphosphine oxide compound is preferable, and a monoacylphosphine oxide compound (particularly preferably 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (for example, DAROCUR TPO or LUCIRIN TPO)) or a bisacylphosphine oxide compound (particularly preferably bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (for example, IRGACURE 819)) is more preferable.

In the water dispersion of the present disclosure, an amount of the included photopolymerization initiator is preferably 0.5 mass % to 12 mass % with respect to a total solid content of the gel particles.

In a case where an amount of the included photopolymerization initiator is 0.5 mass % or greater, sensitivity is more enhanced, and as a result, fixing properties and the like are enhanced.

In view of fixing properties and the like, an amount of the included photopolymerization initiator is more preferably 2.0 mass % or greater, even more preferably 4.0 mass % or greater, and particularly preferably 5.0 mass % or greater.

In a case where the amount of the included photopolymerization initiator is 12 mass % or less, dispersion stability of the gel particles are enhanced, and as a result, preservation stability of the water dispersion liquid is enhanced.

In view of preservation stability and the like, an amount of the photopolymerization initiator is preferably 10 mass % or less and more preferably 8.0 mass % or less.

(Polymerizable Group)

The gel particles have a polymerizable group.

An aspect in which the gel particles have a polymerizable group and preferable ranges of the polymerizable group are as described above.

(Polymerizable Monomer)

In view of adhesiveness and hardness of the film, the gel particles preferably include a polymerizable monomer (that is, a monomer having a polymerizable group).

Even in a case where the three-dimensional crosslinked structure does not have a polymerizable group as a portion of the corresponding structure, the gel particles include a polymerizable monomer, the polymerizable group of the included polymerizable monomer functions as the polymerizable group of the gel particles.

The polymerizable monomer (hereinafter, referred to as “inclusion polymerizable monomer”) included in the gel particles is preferably a polymerizable monomer having an ethylenically unsaturated bond that can perform radical polymerization.

Examples of the polymerizable monomer having an ethylenically unsaturated bond that can perform radical polymerization used as the inclusion polymerizable monomer include a compound having an ethylenically unsaturated group, acrylonitrile, styrene, and various radical polymerizable monomers such as unsaturated polyester, unsaturated polyether, unsaturated polyamide, and unsaturated urethane.

The inclusion polymerizable monomer is preferably a monomer having an ethylenically unsaturated group.

The inclusion polymerizable monomer is used singly or two or more kinds thereof may be used in combination.

In view of adhesiveness and hardness of the film, the inclusion polymerizable monomer is preferably a (meth)acrylate monomer.

Examples of the (meth)acrylate monomer include an acrylate monomer such as 2-hydroxyethyl acrylate, butoxyethyl acrylate, carbitol acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, tridecyl acrylate, 2-phenoxyethyl acrylate, bis(4-acryloxypolyethoxyphenyl) propane, polyethylene glycol diacrylate, polypropylene glycol diacrylate, dipentaerythritol tetraacrylate, trimethylolpropane triacrylate (for example, A-TMPT manufactured by Shin-Nakamura Chemical Co., Ltd.), pentaerythritol triacrylate (for example, A-TMM-3L manufactured by Shin-Nakamura Chemical Co., Ltd.), pentaerythritol tetraacrylate (for example, A-TMMT manufactured by Shin-Nakamura Chemical Co., Ltd.), ditrimethylolpropane tetraacrylate (for example, AD-TMP manufactured by Shin-Nakamura Chemical Co., Ltd.), dipentaerythritol pentaacrylate (for example, SR-399E manufactured by Sartomer), dipentaerythritol hexaacrylate (for example, A-DPH manufactured by Shin-Nakamura Chemical Co., Ltd.), oligoester acrylate, N-methylol acrylamide, diacetone acrylamide, epoxy acrylate, isobornyl acrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, dicyclopentanyl acrylate, and neopentyl glycol propylene oxide adduct diacrylate (NPGPODA); KAYARAD (Registered trademark) DPEA-12 manufactured by Nippon Kayaku Co., Ltd., and VISCOAT (Registered trademark)#802 manufactured by Osaka Organic Chemical Industry Ltd.; and

a methacrylate monomer such as methyl methacrylate, n-butyl methacrylate, allyl methacrylate, glycidyl methacrylate, benzyl methacrylate, dimethylaminomethyl methacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, 2,2-bis(4-methacryloxypolyethoxyphenyl) propane, and trimethylolpropane trimethacrylate (for example, TMPT manufactured by Shin-Nakamura Chemical Co., Ltd.).

Among these (meth)acrylate monomers, trimethylolpropane triacrylate, pentaerythritol triacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, and neopentyl glycol propylene oxide adduct diacrylate are preferable, and dipentaerythritol pentaacrylate is more preferable.

In view of crosslinking properties and film hardness (for example, film hardness. the same is applied in the followings), the inclusion polymerizable monomer is preferably a polyfunctional polymerizable monomer, more preferably a trifunctional or higher functional polymerizable monomer (preferably trifunctional or higher functional (meth)acrylate monomer), and even more preferably a tetrafunctional or higher functional polymerizable monomer (preferably tetrafunctional or higher functional (meth)acrylate monomer).

In view of reactivity in a case of photocuring, a (meth)acrylate monomer is preferably an acrylate monomer.

That is, in view of crosslinking properties, film hardness, and reactivity in a case of photocuring, a trifunctional or higher functional acrylate monomer is preferable, and a tetrafunctional or higher functional acrylate monomer is more preferable.

In addition to the above inclusion polymerizable monomer, commercially available products disclosed in “Handbook of Crosslinking Agent” edited by Yamashita, Shinzo (1981, Taiseisha, Ltd.); “UV.EB Curing Handbook (Raw materials section)” edited by Kato, Kiyomi (1985, Kobtmshi Kankokai); page 79 of “Applications and Markets of UV.EB Curing Technology” edited by RadTech Japan (1989, CMC Publishing, Inc.); “Handbook of Polyester Resins” written by Takiyama, Eiichiro, (1988, Nikkan Kogyo Shimbun, Ltd.); and the like and radical polymerizable or crosslinking monomers well-known in the industry can be used.

For example, photocurable polymerizable monomers used in a photopolymerizable composition disclosed in JP1995-159983A (JP-H07-159983A), JP1995-31399B (JP-H07-31399B), JP1996-224982A (JP-H08-224982A), JP1998-863A (JP-H10-863A), JP1997-134011A (JP-H09-134011A), and JP2004-514014A are known as the inclusion polymerizable monomer, and these can be also included in the gel particles according to the present disclosure.

As the inclusion polymerizable monomer, commercially available products on the market may be used. Examples thereof include urethane acrylate such as AH-600, AT-600, UA-306H, UA-306T, UA-306I, UA-510H, UF-8001G and DAUA-167 (manufactured by Kyoeisha Chemical Co., Ltd.) and UV-1700B, UV-6300B, UV-7550B, UV7600B, UV-7605B, UV-7620EA, UV-7630B, UV-7640B, UV-7650B, UV-6630B, UV7000B, UV-7510B, UV-7461TE, UV-2000B, UV-2750B, UV-3000B, UV-3200B, UV-3210EA, UV-3300B, UV-3310B, UV-3500BA, UV-3520TL, UV-3700B, and UV-6640B (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), ethoxylated or propoxylated acrylate such as SR415, SR444, SR454, SR492, SR499, CD501, SR502, SR9020, CD9021, SR9035, and SR494 (manufactured by Sartomer), and an isocyanur monomer such as A-9300 and A-9300-1CL (manufactured by Shin-Nakamura Chemical Co., Ltd.).

A weight-average molecular weight of the inclusion polymerizable monomer is preferably 100 to 100,000, more preferably 100 to 30,000, even more preferably 100 to 10,000, even more preferably 100 to 1,000, even more preferably 100 to 900, even more preferably 100 to 800, and even more preferably 150 to 700.

In a case where the gel particles include an inclusion polymerizable monomer, the content of the inclusion polymerizable monomer is preferably 0.1 mass % to 75 mass %, more preferably 1 mass % to 65 mass %, even more preferably 10 mass % to 60 mass %, and even more preferably 20 mass % to 50 mass % with respect to the total solid content of the gel particles. In a case where the content thereof is in this range, crosslinking properties and film hardness are enhanced.

(Hydrophilic Group)

The gel particles have a hydrophilic group.

An aspect in which gel particles have a hydrophilic group and a preferable range of a hydrophilic group are as described above.

(Compound Having Hydrophilic Group)

Specific examples of an aspect in which gel particles have a hydrophilic group include an aspect in which the gel particles include at least one kind of compounds having a hydrophilic group independently from a three-dimensional crosslinked structure.

The compound having a hydrophilic group is preferably a compound having a group represented by W¹ in Unit (W).

The compound having a hydrophilic group is preferably a surfactant having a long-chain hydrophobic group, in addition to the hydrophilic group.

As the surfactant, for example, surfactants disclosed in “Surfactant Handbook” (Ichiro Nishi et al., published by Sangyo Tosho Co., Ltd., (1980)) may be used.

Specific examples of the surfactant include alkyl sulfate having a salt of the sulfate group as a hydrophilic group, alkyl sulfonate having a salt of the sulfo group as a hydrophilic group, and alkyl benzene sulfonate having a salt of the sulfo group as a hydrophilic group.

Among these, alkyl sulfate is preferable, alkyl sulfate having an alkyl group having 8 to 20 carbon atoms (more preferably 12 to 18 carbon atoms) is more preferable, and sodium dodecyl sulfate or sodium hexadecyl sulfate are even more preferable.

Examples of the compound having a hydrophilic group include the above compounds exemplified as a monomer for forming Unit (W).

That is, the compounds as a monomer for forming Unit (W) may be included in the gel particles as the portion other than the three-dimensional crosslinked structure, instead of being used as raw materials for forming the three-dimensional crosslinked structure or in addition to the use as a raw material for forming a three-dimensional crosslinked structure.

In addition to the above, an isocyanate compound to which a hydrophilic group is added can be used as a compound having a hydrophilic group.

Examples of the isocyanate compound to which a hydrophilic group is added include an adduct of trimethylolpropane (TMP), xylene diisocyanate (XDI), and polyethylene glycol monomethyl ether (EO) (manufactured by Mitsui Chemicals, Inc., TAKENATE (Registered trademark) D-116N) and a reaction product (an isocyanate compound including a carboxyl group) of 2,2-bis(hydroxymethyl) propionic acid (DMPA) and isophorone diisocyanate (IPDI).

In addition to the above, examples of the compound having a hydrophilic group include the following compounds.

<Total Solid Content of Gel Particles>

The total solid content of the gel particles in the water dispersion of the present disclosure is preferably 1 mass % to 50 mass %, more preferably 3 mass % to 40 mass %, and even more preferably 5 mass % to 30 mass %, with respect to the total amount of the water dispersion.

In a case where the total solid content of the gel particles is 1 mass % or greater, adhesiveness and hardness of the film are enhanced.

In a case where the total solid content of the gel particles is 50 mass % or less, the preservation stability is enhanced.

The total solid content of the gel particles is a value also including components such as a photopolymerization initiator existing inside the gel particles (in gaps of the three-dimensional crosslinked structure).

The total solid content of the gel particles in the water dispersion of the present disclosure is preferably 50 mass % or greater, more preferably 60 mass % or greater, even more preferably 70 mass % or greater, even more preferably 80 mass % or greater, and even more preferably 85 mass % or greater with respect to the total solid content of the water dispersion.

The upper limit of the total solid content of the gel particles may be 100 mass % with respect to the total solid content of the water dispersion. In a case where the water dispersion includes a solid component in addition to the gel particles, the upper limit thereof is preferably 99 mass % or less and more preferably 95 mass % or less.

<Water>

The water dispersion of the present disclosure includes water as a dispersion medium of the gel particles.

That is, since the water dispersion of the present disclosure is an aqueous composition, the water dispersion of the present disclosure is excellent in reduction of environmental impact and workability, compared with the solvent-based composition.

The amount of water in the water dispersion of the present disclosure is not particularly limited. However, the amount thereof is preferably 10 mass % to 99 mass %, more preferably 20 mass % to 95 mass %, even more preferably 30 mass % to 95 mass %, even more preferably 50 mass % to 95 mass %, even more preferably 60 mass % to 95 mass %, and particularly preferably 70 mass % to 90 mass % with respect to the total amount of the water dispersion.

<Colorant>

The water dispersion of the present disclosure may include at least one colorant.

In a case where the water dispersion includes a colorant, the colorant may be included in the gel particles or may not be included in the gel particles.

The colorant is not particularly limited and can be arbitrarily selected from well-known colorants such as a pigment, a water soluble dye, and a dispersed dye. Among these, in view of excellent weather fastness and opulent color reproducibility, it is more preferable that a pigment is included as the colorant.

The pigment is not particularly limited, and can be appropriately selected depending on the purposes. Examples of the pigment include well-known organic pigments and inorganic pigments, and also include resin particles colored with a dye, a commercially available pigment dispersion, or a surface-treated pigment (for example, a dispersion obtained by dispersing a pigment as a dispersion medium in water, a liquid compound, or an insoluble resin and a dispersion obtained by treating a pigment surface with a resin or a pigment derivative).

Examples of the organic pigment and the inorganic pigment include a yellow pigment, a red pigment, a magenta pigment, a blue pigment, a cyan pigment, a green pigment, an orange pigment, a violet pigment, a brown pigment, a black pigment, and a white pigment.

In a case where the pigment is used as a colorant, in a case where pigment particles are prepared, a pigment dispersing agent may be used, if necessary.

With respect to the colorant and pigment dispersing agent such as a pigment, paragraphs 0180 to 0200 of JP2014-040529A can be suitably referred to.

<Sensitizer>

The water dispersion of the present disclosure may contain a sensitizer.

It is preferable that the sensitizer is further included in the gel particles.

In a case where the water dispersion of the present disclosure contains a sensitizer, decomposition of the photopolymerization initiator due to the irradiation with active energy rays can be promoted.

The sensitizer is a material that absorbs specific active energy rays and in an electron excited state.

The sensitizer in an electron excited state comes into contact with a photopolymerization initiator and generates an action such as electron transfer, energy transfer, heat generation. Accordingly, a chemical change of the photopolymerization initiator, that is, decomposition or generation of a radical, an acid, or a base is promoted.

Examples of the well-known sensitizers that can be used together include benzophenone, thioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone, anthraquinone, 9,10-dibutoxyanthracene, a 3-acylcoumarin derivative, terphenyl, styrylketone, 3-(aroylmethylene) thiazoline, camphorquinone, eosin, rhodamine, and erythrosine.

As the sensitizer, a compound represented by Formula (i) disclosed in JP2010-24276A or a compound represented by Formula (I) disclosed in JP1994-107718A (JP-H06-107718A) can be suitably used.

The sensitizer is preferably benzophenone, thioxanthone, isopropyl thioxanthone, 2,4-diethylthioxanthone, or 9,10-dibutoxyanthracene.

In view of suitability to LED light and reactivity with the photopolymerization initiator, the sensitizer is preferably benzophenone, thioxanthone, or isopropyl thioxanthone, more preferably thioxanthone or isopropyl thioxanthone, and particularly preferably isopropyl thioxanthone.

In a case where the water dispersion of the present disclosure contains a sensitizer, the amount of the sensitizer is preferably 0.1 mass % to 25 mass %, more preferably 0.1 mass % to 20 mass %, even more preferably 0.1 mass % to 15 mass %, and particularly preferably 0.1 mass % to 5 mass % with respect to the total solid content of the gel particles.

In a case where the amount of the sensitizer is 0.1 mass % or greater, sensitivity is enhanced, and as a result, fixing properties and the like are enhanced.

In view of fixing properties and the like, the amount of the sensitizer is more preferably 0.3 mass % or greater, even more preferably 0.5 mass % or greater, and particularly preferably 0.8 mass % or greater.

In a case where the amount of the sensitizer is 25 mass % or less (more preferably 20 mass % or less, even more preferably 15 mass % or less, and particularly preferably 5 mass % or less), the dispersion stability of the gel particles is enhanced, and as a result, preservation stability of the water dispersion liquid is enhanced.

In view of the preservation stability and the like, the amount of the sensitizer is even more preferably 4 mass % or less and particularly preferably 3 mass % or less.

<Other Components>

The water dispersion of the present disclosure may contain other components in addition to the above.

The other components may be included in the gel particles and may not be included in the gel particles.

(Polymerization Inhibitor)

The water dispersion of the present disclosure may contain a polymerization inhibitor.

In a case where the water dispersion of the present disclosure contains a polymerization inhibitor, preservation stability of the water dispersion can be further enhanced.

Examples of the polymerization inhibitor include p-methoxyphenol, quinones (hydroquinone, benzoquinone, and methoxybenzoquinone), phenothiazine, catechols, alkylphenols (dibutylhydroxytoluene (BHT)), alkyl bisphenols, zinc dimethyldithiocarbamate, copper dimethyldithiocarbamate, copper dibutyldithiocarbamate, copper salicylate, thiodipropionic acid esters, mercaptobenzimidazole, phosphites, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), 2,2,6,6-tetramethyl-4-hydroxypiperidin-1-oxyl (TEMPOL), cupferron Al, and tris(N-nitroso-N-phenylhydroxylamine) aluminum salt.

Among these, p-methoxyphenol, catechols, quinones, alkylphenols, TEMPO, TEMPOL, cupferron Al, and tris(N-nitroso-N-phenylhydroxylamine) aluminum salt are preferable, and p-methoxyphenol, hydroquinone, benzoquinone, BHT, TEMPO, TEMPOL, cupferron Al, and tris(N-nitroso-N-phenylhydroxylamine) aluminum salt is more preferable.

(Ultraviolet Absorbing Agent)

The water dispersion of the present disclosure may contain an ultraviolet absorbing agent.

In a case where the water dispersion of the present disclosure contains an ultraviolet absorbing agent, weather fastness of the film can be enhanced.

Examples of the ultraviolet absorbing agent include the well-known ultraviolet absorbing agent, for example, a benzotriazole-based compound, a benzophenone-based compound, a triazine-based compound, and a benzoxazole-based compound.

(Solvent)

The water dispersion of the present disclosure may contain an organic solvent.

In a case where the water dispersion of the present disclosure contains a solvent, adhesiveness between the film and the base material can be enhanced.

In a case where the water dispersion of the present disclosure contains a solvent, the content of the solvent is preferably 0.1 mass % to 10 mass % and more preferably 1 mass % to 10 mass % with respect to a total amount of the water dispersion.

Specific examples of the organic solvent are as follows.

-   -   Alcohols (for example, methanol, ethanol, propanol, isopropanol,         butanol, isobutanol, secondary butanol, tertiary butanol,         pentanol, hexanol, cyclohexanol, and benzyl alcohol),     -   Polyhydric alcohols (for example, ethylene glycol, diethylene         glycol, triethylene glycol, polyethylene glycol, propylene         glycol, dipropylene glycol, polypropylene glycol, butylene         glycol, hexanediol, pentanediol, glycerin, hexanetriol,         thiodiglycol, and 2-methyl propanediol),     -   Polyhydric alcohol ethers (for example, ethylene glycol         monomethyl ether, ethylene glycol monoethyl ether, ethylene         glycol monobutyl ether, diethylene glycol monoethyl ether,         diethylene glycol monomethyl ether, diethylene glycol monobutyl         ether, propylene glycol monomethyl ether, propylene glycol         monobutyl ether, tripropylene glycol monomethyl ether,         dipropylene glycol monomethyl ether, dipropylene glycol dimethyl         ether, ethylene glycol monomethyl ether acetate, triethylene         glycol monomethyl ether, triethylene glycol monoethyl ether,         triethylene glycol monobutyl ether, ethylene glycol monophenyl         ether, and propylene glycol monophenyl ether),     -   Amines (for example, ethanolamine, diethanolamine,         triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine,         morpholine, N-ethylmorpholine, ethylenediamine,         diethylenediamine, triethylenetetramine, tetraethylenepentamine,         polyethyleneimine, pentamethyl diethylenetriamine, and         tetramethylpropylenediamine),     -   Amides (for example, formamide, N,N-dimethylformamide, and         N,N-dimethylacetamide),     -   Heterocyclic rings (for example, 2-pyrrolidone,         N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, 2-oxazolidone,         1,3-dimethyl-2-imidazolidinone, and γ-butyrolactone),     -   Sulfoxides (for example, dimethylsulfoxide),     -   Sulfones (for example, sulfolane), and     -   Other (urea, acetonitrile, and acetone)

(Other Surfactants)

The water dispersion of the present disclosure may contain other surfactants, in addition to the above surfactants (alkyl sulfate, alkyl sulfonate, and alkyl benzene sulfonate).

Examples of the other surfactants include surfactants disclosed in JP1987-173463A (JP-S62-173463A) and JP1987-183457A (JP-S62-183457A). Examples thereof include a nonionic surfactant such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, and a polyoxyethylene⋅polyoxypropylene block copolymer.

As the surfactant, an organic fluoro compound may be used.

The organic fluoro compound is preferably hydrophobic. Examples of the organic fluoro compound include a fluorine-based surfactant, an oily fluorine-based compound (for example, fluorine oil), and a solid-like fluorine-based compound resin (for example, tetrafluoroethylene resin), and include compounds disclosed in JP1982-9053A (JP-S57-9053A) (Sections 8 to 17), JP1987-135826B (JP-S62-135826B).

In view of film properties, adhesiveness, and jettability control, the water dispersion of the present disclosure may contain a photopolymerization initiator, a polymerizable compound, a water soluble resin, and a water-dispersible resin outside the gel particles, if necessary.

Here, the expression “a water dispersion contains a photopolymerization initiator outside the gel particles” means that the water dispersion contains a photopolymerization initiator that is not included in the gel particles. The same is applied to a case of a polymerizable compound, a water soluble resin, a water-dispersible resin, and the like are contained outside the gel particles.

(Photopolymerization Initiator that can be Contained Outside Gel Particles)

Examples of the photopolymerization initiator that can be contained outside the gel particles include photopolymerization initiators which are the same as the above photopolymerization initiators (photopolymerization initiator included in the gel particles). As the photopolymerization initiator that can be contained outside the gel particles, a water-soluble or water-dispersible photopolymerization initiator is preferable. In this point of view, preferable examples thereof include DAROCUR (Registered trademark) 1173, IRGACURE (Registered trademark) 2959, IRGACURE (Registered trademark) 754, DAROCUR (Registered trademark) MBF, IRGACURE (Registered trademark) 819DW, IRGACURE (Registered trademark) 500 (above manufactured by BASF SE).

The expression “water solubility” in the photopolymerization initiator that can be contained outside the gel particles refers to properties in which a dissolution amount to 100 g of distilled water at 25° C. in a case where drying is performed for two hours at 105° C. exceeds 1 g.

The expression “water dispersibility” in the photopolymerization initiator that can be contained outside the gel particles means properties which are water insoluble and dispersed in water. Here, the expression “water insoluble” refers to properties in which a dissolution amount to 100 g of distilled water at 25° C. is 1 g or less in a case where the compound is dried at 105° C. for two hours.

(Polymerizable Compound that can be Contained Outside Gel Particles)

Examples of the polymerizable compound that can be contained outside the gel particles include a compound having an ethylenically unsaturated group and a radical polymerizable compound such as acrylonitrile, styrene, unsaturated polyester, unsaturated polyether, unsaturated polyamide, and unsaturated urethane.

Among these, a compound having an ethylenically unsaturated group is preferable, and a compound having a (meth)acryloyl group is particularly preferable.

As the polymerizable compound that can be contained outside the gel particles, a water-soluble or water-dispersible polymerizable compound is preferable.

The “water solubility” in the polymerizable compound that can be contained outside the gel particles is the same as the above “water solubility” in the “photopolymerization initiator that can be contained outside the gel particles”, and the “water dispersibility” in the polymerizable compound that can be contained outside the gel particles is the same as the above “water dispersibility” in the “photopolymerization initiator that can be contained outside the gel particles”.

In view of water solubility or water dispersibility, as the polymerizable compound, a compound having at least one selected from an amide structure, a polyethylene glycol structure, a polypropylene glycol structure, a carboxyl group, and a salt of the carboxyl group is preferable.

In view of the water solubility or water dispersibility, as the polymerizable compound that can be contained outside the gel particles, for example, (meth)acrylic acid, sodium (meth)acrylate, potassium (meth)acrylate, N,N-dimethylacrylamide, N,N-diethylacrylamide, morpholine acrylamide, N-2-hydroxyethyl (meth)acrylamide, N-vinyl pyrrolidone, N-vinyl caprolactam, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, glycerin monomethacrylate, N-[tris(3-acryloylaminopropyloxymethylene)methyl]acrylamide, diethylene glycol bis(3-acryloylaminopropyl) ether, polyethylene glycol di(meth)acrylate, or polypropylene glycol di(meth)acrylate is preferable, and (meth)acrylic acid, N,N-dimethylacrylamide, N-2-hydroxyethyl (meth)acrylamide, 2-hydroxyethyl (meth)acrylate, glycerin monomethacrylate, N-[tris(3-acryloylaminopropyloxymethylene)methyl]acrylamide, diethylene glycol bis(3-acryloylaminopropyl) ether, polyethylene glycol di(meth)acrylate, or polypropylene glycol di(meth)acrylate is more preferable.

(Water Soluble Resin or Water-Dispersible Resin that can be Contained Outside the Gel Particles)

The structures of the water soluble resin or the water-dispersible resin that can be contained outside the gel particles are not particularly limited, and may be any structures.

Examples of the water soluble resin or the water-dispersible resin that can be contained outside the gel particles include a chain-shaped structure, a ramified (branched) structure, a star-shaped structure, a crosslinked structure, and a mesh-shaped structure.

The expression “water soluble” in the water soluble resin that can be contained outside the gel particles has the same meaning as that of the expression “water soluble” in the “photopolymerization initiator that can be contained outside the gel particles”, and the expression “water dispersibility” in the water-dispersible resin that can be contained outside the gel particles has the same meaning as that of the expression “water dispersibility” in the “photopolymerization initiator that can be contained outside the gel particles”.

As the water soluble resin or the water-dispersible resin, a resin having a functional group selected from a carboxy group, a salt of the carboxyl group, a sulfo group, a salt of the sulfo group, a sulfuric acid group, a salt of the sulfuric acid group, a phosphonic acid group, a salt of the phosphonic acid group, a phosphoric acid group, a salt of the phosphoric acid group, an ammonium salt group, a hydroxyl group, a carboxylic acid amide group, and an alkyleneoxy group is preferable.

As the counter cation of the salt, an alkali metal cation such as sodium and potassium, an alkali earth metal cation such as calcium and magnesium, an ammonium cation, or a phosphonium cation is preferable, an alkali metal cation is particularly preferable.

As an alkyl group included in an ammonium group of an ammonium salt group, a methyl group or an ethyl group is preferable.

As the counter anion of the ammonium salt group, a halogen anion such as chlorine and bromine, a sulfate anion, a nitrate anion, a phosphate anion, a sulfonate anion, a carboxylate anion, or a carbonate anion is preferable, and a halogen anion, a sulfonate anion, or a carbonate anion is particularly preferable.

As a substituent on the nitrogen atom of the carboxylic acid amide group, an alkyl group having 8 or less carbon atoms is preferable, and an alkyl group having 6 or less carbon atoms is particularly preferable.

The resin having an alkyleneoxy group preferably has an alkyleneoxy chain consisting of repetition of an alkyleneoxy group. The number of the alkyleneoxy groups included in the alkyleneoxy chain is preferably 2 or greater and particularly preferably 4 or greater.

<Preferable Physical Properties of Water Dispersion>

In a case where the water dispersion is at 25° C. to 50° C., the viscosity of the water dispersion of the present disclosure is preferably 3 mPa·s to 15 mPa·s and more preferably 3 mPa·s to 13 mPa·s. Particularly, as the water dispersion of the present disclosure, the water dispersion of which viscosity at 25° C. is 50 mPa·s or less is preferable. In a case where the viscosity of the water dispersion is in the above range, high jetting stability can be realized in a case where the water dispersion is applied to ink jet recording.

The viscosity of the water dispersion is obtained by using a viscometer: VISCOMETER TV-22 (manufactured by Toki Sangyo Co., Ltd.).

The method of producing the water dispersion of the present disclosure is not particularly limited, as long as the method is a method of capable of dispersing gel particles having a three-dimensional crosslinked structure including Unit (1) and a urea bond, having a hydrophilic group and a polymerizable group, and including a photopolymerization initiator in water.

In view of easiness of obtaining the water dispersion of the present disclosure, the method of producing the water dispersion of the present disclosure is preferably a method of producing a water dispersion of gel particles of this embodiment.

[Method of Producing Water Dispersion of Gel Particles]

A method of producing the water dispersion of gel particles according to the present embodiment (hereinafter, referred to as a “producing method of the present embodiment”) including: a preparation step of preparing an isocyanate group-containing polymer including Unit (1) and an isocyanate group;

an emulsification step of obtaining an emulsion by mixing an oil phase component including the isocyanate group-containing polymer, a photopolymerization initiator, and an organic solvent and a water phase component including water and performing emulsification; and

a gelation step of obtaining a water dispersion of gel particles by heating the emulsion and causing the isocyanate group-containing polymer and water to react each other.

The producing method of the present embodiment may have other steps, if necessary.

It is possible to easily produce the water dispersion of the present disclosure by the producing method of the present embodiment. Particularly, it is possible to produce the gel particles including a photopolymerization initiator by causing both of the isocyanate group-containing polymer and the photopolymerization initiator to be contained in the oil phase component.

<Preparation Step>

According to the present embodiment, a preparation step is a step defined for convenience and is a step of preparing an isocyanate group-containing polymer including Unit (1) and an isocyanate group.

The isocyanate group-containing polymer is as described above as the raw materials of the three-dimensional crosslinked structure.

According to the present embodiment, in the producing of the water dispersion, an isocyanate group-containing polymer prepared in advance may be used, or an isocyanate group-containing polymer may be produced in a case of producing the water dispersion.

The isocyanate group-containing polymer is as described above as the raw materials of the three-dimensional crosslinked structure.

The preparation step may include a stage of producing the isocyanate group-containing polymer including at least one of Units (1-2) and (1-3), in addition to Unit (1).

The isocyanate group-containing polymer including Unit (I-2) can be produced in the well-known producing methods.

The isocyanate group in Unit (I-2) may be a group (that is, a group included in a monomer for forming Unit (I-2)) existing before the polymerization and may be a group added after the polymerization.

As the method of adding the isocyanate group in Unit (I-2) after the polymerization, examples of the method of producing the isocyanate group-containing polymer including Unit (I-2) include:

a method of adding (that is, obtaining an isocyanate group-containing polymer) an isocyanate group by producing a hydroxyl group-containing polymer including a hydroxyl group by polymerization, and

causing the hydroxyl group-containing polymer and a difunctional or higher functional isocyanate compound (that is, a compound including two or more isocyanate groups in one molecule) to react with each other, and adding (that is, obtaining an isocyanate group-containing polymer) an isocyanate group.

According to this reaction, an isocyanate group is introduced to the polymer via a urethane bond.

The hydroxyl group-containing polymer preferably includes Unit (1) and a structural unit (hereinafter, referred to as “Unit (HP-2)”) represented by Formula (HP-2).

In Formula (HP-2), R²¹, X²², and L²² are the same respectively as R²¹, X²², and L²² in Formula (2A), and preferable ranges are also the same.

A preferable aspect (also including a preferable range of the content of Unit (1)) of Unit (1) in a hydroxyl group-containing polymer is the same as the preferable aspect (also including the preferable range of the content of Unit (1)) of Unit (1) in the isocyanate group-containing polymer.

A preferable content of Unit (HP-2) in a hydroxyl group-containing polymer is the same as the preferable range of the content of Unit (I-2) in the isocyanate group-containing polymer.

In view of producing easiness and availability, the difunctional or higher functional isocyanate compound is preferably a difunctional isocyanate compound.

Examples of the difunctional isocyanate compound include isophorone diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, 1,3-bis(isocyanatomethyl) cyclohexane, m-xylylene diisocyanate, and dicyclohexylmethane-4,4′-diisocyanate.

Examples of the method of producing the isocyanate group-containing polymer including Unit (I-2) include a method of using an isocyanate group-containing monomer, as one of the raw materials of the isocyanate group-containing polymer. In this method, an isocyanate group-containing polymer is obtained by copolymerizing a monomer for at least forming Unit (1) and an isocyanate group-containing monomer.

As the isocyanate group-containing monomer, a compound represented by Formula (IM) is preferable.

In Formula (IM), R²¹, X²², and L²² are the same respectively as R²¹, X²², and L²² in Formula (2A), and preferable ranges are also the same.

The isocyanate group-containing polymer including Group (I-3) can be produced by the well-known producing method.

The isocyanate group in Group (I-3) may be a group (that is, a group included in the monomer for forming Group (I-3)) existing before the polymerization or may be a group added after the polymerization.

As the method of adding the isocyanate group in Group (I-3) after the polymerization, examples of the method of producing the isocyanate group-containing polymer including Group (I-3) include:

a method of adding (that is, obtaining an isocyanate group-containing polymer) an isocyanate group, by producing a polymer including Unit (1),

producing a hydroxyl group-containing polymer by reacting a compound represented by (HP-3) with a polymer including Unit (1), and

causing the hydroxyl group-containing polymer and the difunctional or higher functional isocyanate compound to react with each other and adding (that is, obtaining an isocyanate group-containing polymer) an isocyanate group.

According to this reaction, an isocyanate group is introduced to a polymer via a urethane bond.

In Formula (HP-3), Z³¹ and n are the same respectively as Z³¹ and n in Formula (3), and preferable ranges are also the same.

<Oil Phase Component>

The oil phase component includes an isocyanate group-containing polymer, a photopolymerization initiator, and an organic solvent.

Examples of the organic solvent included in the oil phase component include ethyl acetate, methyl ethyl ketone, and acetone.

The isocyanate group-containing polymer included in the oil phase component is as described above in the raw materials of the three-dimensional crosslinked structure.

The isocyanate group-containing polymer may be included in the oil phase component singly or two or more kinds thereof may be included in the oil phase component.

In the producing method of the present embodiment, a content (total content in a case where two or more kinds are used) of the isocyanate group-containing polymer is preferably 10 mass % to 98 mass %, more preferably 20 mass % to 95 mass %, even more preferably 30 mass % to 90 mass %, even more preferably 30 mass % to 80 mass %, and particularly preferably 30 mass % to 70 mass % with respect to the total amount (total solid content) excluding the organic solvent and water from the oil phase component and the water phase component.

In a case where the total amount is 10 mass % or greater, the three-dimensional crosslinked structure is more easily formed.

In a case where the content is 98 mass % or less, the content of the photopolymerization initiator and the like can be easily secured.

In the present specification, a total amount (total solid content) excluding the organic solvent and water from the oil phase component and the water phase component corresponds to a total solid content of the produced gel particles.

The photopolymerization initiator is a component included in the gel particles which is a target product of the producing method of the present embodiment, and is contained in the oil phase component in the raw material stage. Accordingly, the producing of the gel particles including the photopolymerization initiator becomes easier.

The preferable range of the photopolymerization initiator is as described above.

The photopolymerization initiator may be included in the oil phase component singly or two or more kinds thereof may be included in the oil phase component.

A preferable range of the content (total content in a case where two or more kinds are used) of the photopolymerization initiator with respect to the total solid content of the oil phase component and the water phase component is the same as the preferable range of the content (total content in a case where two or more kinds are used) of the photopolymerization initiator with respect to the total solid content of the gel particles.

Even in a case where components in addition to the photopolymerization initiator are included in the gel particles which are a target product, the components are preferably contained in the oil phase component.

For example, in a case where gel particles including a polymerizable monomer are produced, the polymerizable monomer is preferably contained in the oil phase component. In this case, the preferable range of the content (total content in a case where two or more kinds are used) of the polymerizable monomer with respect to the total solid content of the oil phase component and the water phase component is the same as the preferable range of the content (total content in a case where two or more kinds are used) of the polymerizable monomer (inclusion polymerizable monomer) with respect to the total solid content of the gel particles.

In a case where gel particles including the sensitizer are produced, the sensitizer is preferably contained in the oil phase component. In this case, the preferable range of the content (total content in a case where two or more kinds are used) of the sensitizer with respect to the total solid content of the oil phase component and the water phase component is the same as the preferable range of the content (total content in a case where two or more kinds are used) of the sensitizer with respect to the total solid content of the gel particles.

The oil phase component may contain a catalyst.

In a case where the oil phase component includes a catalyst, the reaction in the gelation step more effectively proceeds.

Examples of the catalyst include triethylamine, diisopropylethylamine, 1,4-diazabicyclo[2.2.2]octane, dimethyl benzyl amine, bis(dimethylaminoethyl) ether, N,N-dimethylethanolamine, triethylenediamine, N,N-dimethylcyclohexylamine, pentamethyldiethylenetriamine, N,N,N′,N′,N″-pentamethyldipropylenetriamine, N-ethyl morpholine, N-methyl morpholine, diaminoethoxyethanol, trimethylaminoethylethanolamine, dimethylaminopropylamine, dimorpholino dimethyl ether, and 1,3,5-tris(3-(dimethylamino)propyl)-hexahydro-2-triazine.

Examples of the catalyst include U-CAT (Registered trademark) SA 102 and U-CAT (Registered trademark) SA 1102 manufactured by San-Apro Ltd.

<Water Phase Component>

The water phase component is not particularly limited, as long as the water phase component includes water. The water phase component may be only water.

The component that can be contained in the water phase component includes a compound (hereinafter, referred to as a “hydrophilic group-containing compound”) having a hydrophilic group, in addition to water.

In the producing method of the present embodiment, at least one of the oil phase component or the water phase component preferably includes a hydrophilic group-containing compound. The hydrophilic group-containing compound may be used singly or two or more kinds thereof may be used.

Here, in a case where the isocyanate group-containing polymer has a hydrophilic group (for example, having Unit (W)), the hydrophilic group-containing compound may not be contained in the oil phase component and may not be contained in the water phase component.

In the present embodiment, the hydrophilic group-containing compound may be used singly or two or more kinds thereof may be used.

A first hydrophilic group-containing compound may be contained in an oil phase component, and a second hydrophilic group-containing compound different from the first hydrophilic group-containing compound may be contained in the water phase component.

Each of the first hydrophilic group-containing compound and the second hydrophilic group-containing compound may be used singly and two or more kinds thereof may be used.

In a case where at least one of the oil phase component or the water phase component include a hydrophilic group-containing compound, a content (total content in a case where two or more kinds are used) of the hydrophilic group-containing compound is preferably 0.5 mass % to 20 mass % with respect to the total solid content of the oil phase component and the water phase component.

In a case where the amount of the hydrophilic group-containing compound is 0.5 mass % or greater, dispersibility, redispersibility, and preservation stability are enhanced.

In a case where the amount of the hydrophilic group-containing compound is 20 mass % or less, hardness of the formed film is enhanced.

The amount of the hydrophilic group-containing compound is more preferably 1 mass % to 20 mass % and even more preferably 5 mass % to 20 mass %, with respect to the total solid content.

In a case where the oil phase component includes a compound having a carboxyl group, a sulfo group, a sulfate group, a phosphonic acid group, or a phosphoric acid group as a hydrophilic group-containing compound, the water phase component may contain a neutralizing agent. In this case, in a case where the oil phase component and the water phase component are mixed, a carboxyl group, a sulfo group, a sulfate group, a phosphonic acid group, or a phosphoric acid group are neutralized, and a salt of the carboxyl group, a salt of the sulfo group, a salt of the sulfate group, a salt of the phosphonic acid group, or a salt of the phosphoric acid group are formed. These salts function as hydrophilic groups of gel particles. These salts have particularly excellent in an effect of dispersing gel particles in water.

Examples of the neutralizing agent include sodium hydroxide and potassium hydroxide.

<Emulsification Step>

The emulsification step is a step of obtaining an emulsion by mixing an oil phase component and a water phase component and perform emulsification.

The mixing of the oil phase component and the water phase component and the emulsification of the mixture obtained by the mixing can be performed by well-known methods.

The emulsification can be performed by a disperser such as a homogenizer.

Examples of the rotation speed in the emulsification include 5,000 rpm to 20,000 rpm, and the rotation speed is preferably 10,000 rpm to 15,000 rpm.

Examples of the rotation time in the emulsification include 1 minute to 120 minutes, and the rotation time is preferably 3 minutes to 60 minutes, more preferably 3 minutes to 30 minutes, and particularly preferably 5 minutes to 15 minutes.

<Gelation Step>

The gelation step is a step of obtaining a water dispersion of gel particles by heating the emulsion and causing the isocyanate group-containing polymer and water to react with each other.

According to this reaction, a urea bond is formed, a three-dimensional crosslinked structure including Unit (1) and a urea bond is formed.

Unit (1) is a structural unit included in the isocyanate group-containing polymer.

The heating temperature (reaction temperature) of the emulsion in the gelation step is preferably 35° C. to 70° C. and more preferably 40° C. to 60° C.

The heating time (reaction time) in the gelation step is preferably 6 hours to 50 hours, more preferably 12 hours to 40 hours, and particularly preferably 15 hours to 35 hours.

The gelation step preferably includes a stage of distilling an organic solvent from the emulsion.

The stage of causing the isocyanate group-containing polymer and water to react with each other also functions as a stage of distilling an organic solvent from an emulsion.

The gelation step can include a stage of adding a catalyst to an emulsion. Examples of the catalyst are as described above.

The producing method of the embodiment may have other steps in addition to the preparation step, the emulsification step, and the gelation step, if necessary.

Examples of the other step include a step of adding the other components such as a colorant to the water dispersion of the gel particles obtained in the gelation step.

The other added components are as described above as the other components that can contain the water dispersion.

<Image Forming Method>

The image forming method of the present disclosure has an application step of using the water dispersion of the present disclosure as ink and applying a water dispersion as ink on a recording medium and an irradiation step of irradiating the water dispersion applied on the recording medium with the active energy rays.

In a case where these steps are performed, an image having excellent adhesiveness to a recording medium and excellent hardness is formed on the recording medium. This formed image is also excellent in fixing properties, water resistance, and a solvent resistance.

As the recording medium, the above base materials (plastic base materials and the like) can be used.

(Application Step)

The application step is a step of applying the water dispersion of the present disclosure on the recording medium.

As an aspect of applying the water dispersion to the recording medium, an aspect of applying the water dispersion by an ink jet method is preferable.

The application of the water dispersion by an ink jet method can be performed by using the well-known ink jet recording devices.

An ink jet recording device is not particularly limited, a well-known ink jet recording device that can achieve the desired resolution can be arbitrarily selected to be used.

That is, any one of the well-known ink jet recording devices including a commercially available product can discharge the water dispersion to a recording medium by the image forming method of the present disclosure.

Examples of the ink jet recording device include devices including an ink supplying method, a temperature sensor, and heating means.

Examples of the ink supplying method include an original tank including the water dispersion of the present disclosure, a supply piping, an ink supply tank just before an ink jet head, a filter, and a piezo-type ink jet head. The piezo-type ink jet head can be driven so as to eject multi-sized dots of preferably 1 pl to 100 pl and more preferably 8 pl to 30 pl at a resolution of preferably 320 dpi×320 dpi to 4,000 dpi×4,000 dpi (dot per inch), more preferably 400 dpi×400 dpi to 1,600 dpi×1,600 dpi, and even more preferably 720 dpi×720 dpi. The dpi (dot per inch) according to the present disclosure represents the number of dots per 2.54 cm (1 inch).

(Irradiation Step)

The irradiation step is a step of irradiating the water dispersion applied to the recording medium with the active energy rays.

In a case where the water dispersion applied to the recording medium is irradiated with active energy rays, the crosslinking reaction of the gel particles in the water dispersion proceeds, the image is fixed, and the film hardness of the image can be improved.

Examples of the active energy rays that can be used in the irradiation step include ultraviolet rays (hereinafter, also referred to as UV light), and visible rays, electron beams. Among these, UV light is preferable.

A peak wavelength of the active energy rays (light) is preferably 200 nm to 405 nm, more preferably 220 nm to 390 nm, even more preferably 220 nm to 385 nm, and even more preferably 220 nm to 365 nm.

The peak wavelength thereof is also preferably 200 nm to 310 nm and also preferably 200 nm to 280 nm.

For example, the exposure surface illuminance in a case of irradiation with the active energy rays (light) may be 10 mW/cm² to 2,000 mW/cm² and is preferably 20 mW/cm² to 1,000 mW/cm²·s

As the light source for generating the active energy rays (light), a mercury lamp, a metal halide lamp, a UV fluorescent lamp, a gas laser, a solid-state laser, and the like are widely known.

The replacement of the light sources exemplified above into a semiconductor ultraviolet light emitting device is industrially and environmentally useful.

Among these, among semiconductor ultraviolet light emitting devices, light emitting diode (LED) and a laser diode (LD) are compact, has a long lifetime, high efficiency, and low cost, and is expected as a light source.

As the light source, a metal halide lamp, an extra high pressure mercury lamp, a high pressure mercury lamp, a medium pressure mercury lamp, a low pressure mercury lamp, LED, and a blue-violet laser are preferable.

Among these, an extra high pressure mercury lamp that can perform irradiation with light at a wavelength of 365 nm, 405 nm, or 436 nm, a high pressure mercury lamp that can perform irradiation with light at a wavelength of 365 nm, 405 nm, or 436 nm, LED that can perform irradiation with light at a wavelength of 355 nm, 365 nm, 385 nm, and 395 nm, or 405 nm is more preferable, and LED that can perform irradiation with light at a wavelength of 355 nm, 365 nm, 385 nm, 395 nm, or 405 nm is most preferable.

A photopolymerization initiator that was not able to be used in an aqueous ink in the related art can be used in the water dispersion of the present disclosure by causing the gel particles having the three-dimensional crosslinked structure to be included in the photopolymerization initiator. Particularly, in a case where a photopolymerization initiator such as an acylphosphine compound or a sensitizer such as a thioxanthone compound of which an absorption wavelength is 350 to 450 nm is used, LED is particularly preferable as a light source.

In the irradiation step, the irradiation time of the water dispersion applied on the recording medium with the active energy rays may be 0.01 seconds to 120 seconds and preferably 0.1 seconds to 90 seconds.

With respect to the irradiation condition of the active energy rays and basic irradiation method, conditions disclosed in JP1985-132767A (JP-S60-132767A) can be suitably referred to.

Specifically, a method of scanning the head unit and the light sources by a so-called shuttle method of providing the light sources on both sides of the head unit including the ink ejection device and a method of performing irradiation with active energy rays by a separate light source without driving are preferable as an irradiation method with active energy rays. The irradiation with the active energy rays is preferably performed for a certain period of time (for example, for 0.01 seconds to 120 seconds and preferably for 0.01 seconds to 60 seconds) after water dispersion is landed and dried by heating.

(Heating and Drying Step)

If necessary, the image forming method of the present disclosure may have a heating and drying step of heating and drying the water dispersion on the recording medium before the irradiation step and after the application step.

The heating means for performing heating and drying is not particularly limited. However, examples thereof include a heat drum, hot air, an infrared lamp, a heat oven, and a heat plate.

The heating temperature is preferably 40° C. or higher, more preferably 40° C. to 150° C., and even more preferably 40° C. to 80° C.

The heating time can be appropriately set by adding the composition of the water dispersion, the printing speed, and the like.

EXAMPLES

Hereinafter, the invention is specifically described with reference to the specific examples, but the invention is not limited to the following examples without departing from the gist of the invention.

Unless particularly described otherwise, a “part” is based on mass.

Unless particularly described otherwise, each of the measurements is performed in the temperature condition of 25° C.

With respect to the polymer indicated below, a number applied to the lower right of each of the structural units indicates a copolymerization mass ratio. Here, a number applied to the lower right of an ethyleneoxy group indicates the number of ethyleneoxy groups.

[Synthesis of Isocyanate Group-Containing Polymer]

Isocyanate Group-Containing Polymers P-1 to P-44 which become raw materials of Structure (S-1) to (S-44) (see Table 1 for correspondence to example numbers) which were specific examples of the three-dimensional crosslinked structure were synthesized.

In each of the following examples, in the gelation step, urea bonds were formed by causing isocyanate groups of Isocyanate Group-Containing Polymers P-1 to P-44 and water to react with each other, and accordingly three-dimensional crosslinked structures (Structures (S-1) to (S-44)) having urea bonds were formed.

The structures of Isocyanate Group-Containing Polymers P-1 to P-44 are structures in which urea bonds positioned at terminals of Structures (S-1) to (S-44) are substituted with isocyanate groups (for example, see structures of Isocyanate Group-Containing Polymer P-2 and Structure (S-2)).

Hereinafter, synthesis examples are provided mainly with respect to representatives of Isocyanate Group-Containing Polymers P-1 to P-44.

<Synthesis of Isocyanate Group-Containing Polymer P-2>

Isocyanate Group-Containing Polymer P-2 was synthesized by the following scheme.

Detailed operations of the schemes are as follows.

75.9 g of methyl ethyl ketone was weighed to a 1,000 ml three-neck flask including a cooling pipe and heating and stirring was performed at 75° C. under the nitrogen stream.

Independently from these, a mixed solution prepared by mixing 177.1 g of methyl ethyl ketone (MEK), 90 g of methyl methacrylate, 10 g of 2-isocyanate ethyl methacrylate, and 6.65 g of V-601 (dimethyl 2,2′-azobis(2-methyl propionate), manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise to the flask over two hours. After the dropwise addition was completed and heating was performed for four hours at 75° C., 0.222 g of V-601 was added, stirring was further performed for two hours at 90° C., and reaction was performed. The obtained reaction solution was allowed to cool, and cooling was performed to room temperature.

The concentration of the obtained reaction solution was adjusted by using methyl ethyl ketone, so as to obtain a solution (solid content: 30 mass %) of Isocyanate Group-Containing Polymer P-2.

<Synthesis of Isocyanate Group-Containing Polymer P-1>

Isocyanate Group-Containing Polymer P-1 was synthesized in the same manner as Isocyanate Group-Containing Polymer P-2, except for changing a raw material monomer (methyl methacrylate) in Isocyanate Group-Containing Polymer P-2.

<Synthesis of Isocyanate Group-Containing Polymer P-10>

Hydroxyl Group-Containing Polymer H-10 was synthesized by the following scheme, and Hydroxyl Group-Containing Polymer H-10 synthesized was used so as to synthesize Isocyanate Group-Containing Polymer P-10.

Detailed operations of the scheme are as follows.

(Synthesis of Hydroxyl Group-Containing Polymer H-10)

75.4 g of methyl ethyl ketone was weighed to a 1,000 ml three-neck flask including a cooling pipe and heating and stirring was performed at 75° C. under the nitrogen stream. Independently from this, a mixed solution prepared by mixing 175.9 g of methyl ethyl ketone (MEK), 90 g of methyl methacrylate, 10 g of 2-hydroxyethyl methacrylate, and 6.74 g of V-601 (dimethyl 2,2′-azobis(2-methyl propionate), manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise to the flask over two hours. After the dropwise addition was completed and heating was performed for four hours at 75° C., 0.221 g of V-601 was added, stirring was further performed for two hours at 90° C., and reaction was performed. The obtained reaction solution was allowed to cool, and cooling was performed to room temperature, so as to obtain a solution of Hydroxyl Group-Containing Polymer H-10.

(Synthesis of Isocyanate Group-Containing Polymer P-10)

22.38 g of 1,3-bis(isocyanatomethyl) cyclohexane (cis-, trans-mixture) and 52.23 g of methyl ethyl ketone were further added to the solution of Hydroxyl Group-Containing Polymer H-10, and stirring was performed at room temperature under the nitrogen stream. 0.433 g of NEOSTAN (Registered trademark) U-600 (manufactured by Nitto Kasei Co., Ltd., Inorganic bismuth catalyst) was added thereto, stirring was performed for one hour, the temperature was increased to 50° C., and stirring was further performed for two hours. The concentration of the obtained reaction solution was adjusted by using methyl ethyl ketone, so as to obtain a solution (solid content: 30 mass %) of Isocyanate Group-Containing Polymer P-10.

<Synthesis of Isocyanate Group-Containing Polymers P-3 to P-6, P-11 to P-27, P-31, and P-32>

Each of Isocyanate Group-Containing Polymer P-3 to P-6, P-11 to P-27, P-31, and P-32 was synthesized in the same manner as the synthesis of Isocyanate Group-Containing Polymer P-10 except for changing a raw material monomer in the synthesis of Isocyanate Group-Containing Polymer P-10.

In the synthesis of Isocyanate Group-Containing Polymers P-31 and P-32, a macromonomer “ARONIX (Registered trademark) AA-6” manufactured by Toagosei Co., Ltd. was used as a monomer for forming a structural unit (specific example of Unit (G1)) having a graft chain.

<Synthesis of Isocyanate Group-Containing Polymer P-28>

Hydroxyl Group-Containing Polymer H-28 was synthesized by the following scheme, and Hydroxyl Group-Containing Polymer H-28 synthesized was used, so as to synthesize Isocyanate Group-Containing Polymer P-28.

Detailed operations of the scheme were as follows.

(Synthesis of Hydroxyl Group-Containing Polymer H-28)

76.7 g of methyl ethyl ketone was weighed to a 1,000 ml three-neck flask including a cooling pipe and heating and stirring was performed at 75° C. under the nitrogen stream. Independently from this, a mixed solution prepared by mixing 179 g of methyl ethyl ketone, 100 g of methyl methacrylate, 5 g of 1-thioglycerol, and 2.3 g of V-601 (dimethyl 2,2′-azobis(2-methyl propionate), manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise to the flask over two hours. After the dropwise addition was completed and heating was performed for four hours at 75° C., 0.077 g of V-601 was added, stirring was further performed for two hours at 90° C., and reaction was performed. The obtained reaction solution was allowed to cool, and cooling was performed to room temperature, so as to obtain a solution of Hydroxyl Group-Containing Polymer H-28.

(Synthesis of Isocyanate Group-Containing Polymer P-28)

38 g of TPA-100 (DURANATE (Registered trademark) TPA-100 manufactured by Asahi Kasei Corporation) and 88.6 g of methyl ethyl ketone were further added to the solution of Hydroxyl Group-Containing Polymer H-28, and stirring was performed at room temperature under the nitrogen stream. 0.487 g of NEOSTAN (Registered trademark) U-600 was added thereto, stirring was performed for one hour, the temperature was increased to 50° C., and stirring was further performed for two hours. The concentration of the obtained reaction solution was adjusted by using methyl ethyl ketone, so as to obtain a solution (solid content: 30 mass %) of Isocyanate Group-Containing Polymer P-28.

<Synthesis of Isocyanate Group-Containing Polymers P-7 to P-9, P-29, P-30, and P-39 to P-41>

Each of Isocyanate Group-Containing Polymers P-7 to P-9, P-29, P-30, and P-39 to P-41 was synthesized in the same manner as the synthesis of Isocyanate Group-Containing Polymer P-28 except for changing kinds of the raw material monomers and the like, in the synthesis of Isocyanate Group-Containing Polymer P-28.

In the synthesis of Isocyanate Group-Containing Polymer P-39, PME-4000 (manufactured by NOF Corporation; methoxy polyethylene glycol monomethacrylate (a repetition number of an ethyleneoxy group in one molecule was 90)) was used as a monomer for forming a structural unit including repetition of an ethyleneoxy group.

<Synthesis of Isocyanate Group-Containing Polymer P-34>

A hydroxyl group-containing polymer was synthesized by the following scheme, and Hydroxyl Group-Containing Polymer H-34 synthesized was used, so as to synthesize Isocyanate Group-Containing Polymer P-34.

Detailed operations of the scheme were as follows.

(Synthesis of Hydroxyl Group-Containing Polymer H-34)

75.5 g of methyl ethyl ketone was weighed to a 1,000 ml three-neck flask including a cooling pipe and heating and stirring was performed at 75° C. under the nitrogen stream. Independently from this, a mixed solution prepared by mixing 176.1 g of methyl ethyl ketone, 80 g of methyl methacrylate, 10 g of 2-hydroxyethyl methacrylate, 10 g of methacrylic acid, and 6.85 g of V-601 (dimethyl 2,2′-azobis(2-methyl propionate), manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise to the flask over two hours. After the dropwise addition was completed and heating was performed for four hours at 75° C., 0.228 g of V-601 was added, stirring was further performed for two hours at 90° C., and reaction was performed. The obtained reaction solution was allowed to cool, and cooling was performed to room temperature, so as to obtain a solution of Hydroxyl Group-Containing Polymer H-34.

(Synthesis of Isocyanate Group-Containing Polymer P-34)

22.38 g of 1,3-bis(isocyanatomethyl) cyclohexane (cis-, trans-mixture) and 52.23 g of methyl ethyl ketone were further added to the solution of Hydroxyl Group-Containing Polymer H-34, and stirring was performed at room temperature under the nitrogen stream. 0.433 g of NEOSTAN (Registered trademark) U-600 was added thereto, stirring was performed for one hour, the temperature was increased to 50° C., and stirring was further performed for two hours. The concentration of the obtained reaction solution was adjusted by using methyl ethyl ketone, so as to obtain a solution (solid content: 30 mass %) of Isocyanate Group-Containing Polymer P-34.

<Synthesis of Isocyanate Group-Containing Polymers P-33, P-36 to P-38, P-42, and P-43>

Each of Isocyanate Group-Containing Polymers P-33, P-36 to P-38, P-42, and P-43 was synthesized in the same manner as the synthesis of Isocyanate Group-Containing Polymer P-34 except for changing raw material monomers, in the synthesis of Isocyanate Group-Containing Polymer P-34.

In the synthesis of Isocyanate Group-Containing Polymer P-42 and P-43, a macromonomer “ARONIX (Registered trademark) AA-6” manufactured by Toagosei Co., Ltd. was used as a monomer for forming a structural unit (specific example of Unit (G1)) having a graft chain.

In the synthesis of Isocyanate Group-Containing Polymer P-43, PME-4000 (manufactured by NOF Corporation; methoxy polyethylene glycol monomethacrylate (a repetition number of an ethyleneoxy group in one molecule was 90)) was used as a monomer for forming a structural unit including repetition of an ethyleneoxy group.

<Synthesis of Isocyanate Group-Containing Polymer P-35>

Hydroxyl Group-Containing Polymer H-35 was synthesized by the following scheme, and Hydroxyl Group-Containing Polymer H-35 synthesized was used so as to synthesize Isocyanate Group-Containing Polymer P-35.

Detailed operations of the scheme were as follows.

(Synthesis of Hydroxyl Group-Containing Polymer H-35)

74.9 g of methyl ethyl ketone was weighed to a 1,000 ml three-neck flask including a cooling pipe and heating and stirring was performed at 75° C. under the nitrogen stream. Independently from this, a mixed solution prepared by mixing 174.5 g of methyl ethyl ketone, 90 g of methyl methacrylate, 10 g of 2-hydroxyethyl methacrylate, 10 g of PME-4000 (manufactured by NOF Corporation; methoxy polyethylene glycol monomethacrylate (a repetition number of an ethyleneoxy group in one molecule was 90)), and 6.06 g of V-601 (dimethyl 2,2′-azobis(2-methyl propionate), manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise to the flask over two hours. After the dropwise addition was completed and heating was performed for four hours at 75° C., 0.202 g of V-601 was added, stirring was further performed for two hours at 90° C., and reaction was performed. The obtained reaction solution was allowed to cool, and cooling was performed to room temperature, so as to obtain a solution of Hydroxyl Group-Containing Polymer H-35.

(Synthesis of Isocyanate Group-Containing Polymer P-35)

22.38 g of 1,3-bis(isocyanatomethyl) cyclohexane (cis-, trans-mixture) and 52.23 g of methyl ethyl ketone were further added to the solution of Hydroxyl Group-Containing Polymer H-35, and stirring was performed at room temperature under the nitrogen stream. 0.433 g of NEOSTAN (Registered trademark) U-600 was added thereto, stirring was performed for one hour, the temperature was increased to 50° C., and stirring was further performed for two hours. The concentration of the obtained reaction solution was adjusted by using methyl ethyl ketone, so as to obtain a solution (solid content: 30 mass %) of Isocyanate Group-Containing Polymer P-35.

<Synthesis of Isocyanate Group-Containing Polymer P-44>

Hydroxyl Group-Containing Polymer H-44 was synthesized by the following scheme, and Hydroxyl Group-Containing Polymer H-44 synthesized was used so as to synthesize Isocyanate Group-Containing Polymer P-44.

Detailed operations of the scheme were as follows.

(Synthesis of Hydroxyl Group-Containing Polymer H-44)

75.2 g of methyl ethyl ketone was weighed to a 1,000 ml three-neck flask including a cooling pipe and heating and stirring was performed at 75° C. under the nitrogen stream. Independently from this, a mixed solution prepared by mixing 175.5 g of methyl ethyl ketone, 80 g of methyl methacrylate, 20 g of 2-hydroxyethyl methacrylate, and 6.482 g of V-601 (dimethyl 2,2′-azobis(2-methyl propionate), manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise to the flask over two hours. After the dropwise addition was completed and heating was performed for four hours at 75° C., 0.216 g of V-601 was added, stirring was further performed for two hours at 90° C., and reaction was performed. The obtained reaction solution was allowed to cool, and cooling was performed to room temperature, so as to obtain a solution of Hydroxyl Group-Containing Polymer H-44.

(Synthesis of Isocyanate Group-Containing Polymer P-44)

10.8 g of 2-isocyanate ethyl acrylate was further added to the solution of Hydroxyl Group-Containing Polymer H-44, and 0.433 g of NEOSTAN (Registered trademark) U-600 was added, and stirring was performed for one hour, the temperature was increased to 50° C., and stirring was further performed for one hour. The obtained reaction solution was cooled to the room temperature, 22.38 g of 1,3-bis(isocyanatomethyl) cyclohexane (cis-, trans-mixture) and 52.23 g of methyl ethyl ketone were added, and stirring was performed at room temperature under the nitrogen stream. After the stirring was performed for one hour, the temperature was increased to 50° C., and stirring was further performed for two hours. The concentration of the obtained reaction solution was adjusted by using methyl ethyl ketone, so as to obtain a 30 mass % solution (solid content: 30 mass %) of Isocyanate Group-Containing Polymer P-44.

[Synthesis of Comparative Polymer]

Comparative Polymers C-1 to C-4 used in comparative examples were synthesized.

Comparative Polymers C-1 to C-4 were polymers not containing an isocyanate group.

<Synthesis of Comparative Polymer C-1>

Comparative Polymer C-1 was synthesized by the following scheme.

Detailed operations of the scheme were as follows.

75.1 g of methyl ethyl ketone was weighed to a 500 ml three-neck flask including a cooling pipe and heating and stirring was performed at 75° C. under the nitrogen stream.

Independently from this, a mixed solution prepared by mixing 175.2 g of methyl ethyl ketone, 90 g of methyl methacrylate, 10 g of 1,2-ethanediol 1-acrylate 2-(N-butylcarbamate), 10 g of methacrylic acid, and 6.65 g of V-601 (dimethyl 2,2′-azobis(2-methyl propionate), manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise to the flask over two hours. After the dropwise addition was completed and heating was performed for four hours at 75° C., 0.211 g of V-601 was added, stirring was further performed for two hours at 90° C., and reaction was performed. The obtained reaction solution was allowed to cool, and cooling was performed to room temperature. The concentration of the obtained reaction solution was adjusted by using methyl ethyl ketone, so as to obtain a solution (solid content: 30 mass %) of Comparative Polymer C-1.

<Synthesis of Comparative Polymer C-2>

Comparative Polymer C-2 was synthesized by the following scheme.

Detailed operations of the scheme were as follows.

75.1 g of methyl ethyl ketone was weighed to a 500 ml three-neck flask including a cooling pipe and heating and stirring was performed at 75° C. under the nitrogen stream. Independently from this, a mixed solution prepared by mixing 175.2 g of methyl ethyl ketone, 90 g of butyl methacrylate, 10 g of methacrylic acid, and 6.612 g of V-601 (dimethyl 2,2′-azobis(2-methyl propionate), manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise to the flask over two hours. After the dropwise addition was completed and heating was performed for four hours at 75° C., 0.17 g of V-601 was added, stirring was further performed for two hours at 90° C., and reaction was performed. The obtained reaction solution was allowed to cool, and cooling was performed to room temperature. The concentration of the obtained reaction solution was adjusted by using methyl ethyl ketone, so as to obtain a 30 mass % solution (solid content: 30 mass %) of Comparative Polymer C-2.

<Synthesis of Comparative Polymer C-3 (Urethane Acrylate (a))>

Comparative Polymer C-3 (“Urethane Acrylate (a)” in the publication) was synthesized according to paragraph 0183 of JP2013-199602A.

444.6 parts by mass of isophorone diisocyanate (IPDI) and 202.3 parts by mass of 1,12-dodecanediol were introduced to a reaction vessel including a stirrer, a cooling pipe, a dropping funnel, and an air introduction pipe, 0.26 parts by mass of stannous octoate was added under stirring, and the temperature in the reaction vessel was increased to 90° C., so as to perform reaction for 1.5 hours. After the reaction, 700.0 parts by mass of methoxy PEG1000 (methoxy polyethylene glycol, Toho Chemical Industry Co., Ltd.) and 0.54 parts by mass of tin stannous octoate were added, and reaction was further performed for 1.5 hours. Subsequently, 1300.0 parts of dipentaerythritol pentaacrylate, 1.32 parts of methoquinone, and 1.06 parts of stannous octoate were introduced to the corresponding reaction vessel and were mixed with each other, the temperature in the reaction vessel was increased to 85° C. under air bubbling, and reaction was performed for three hours, and cooling was performed, so as to obtain Comparative Polymer C-3 (Urethane Acrylate (a)).

<Synthesis of Comparative Polymer C-4 (Urethane Acrylate (b))>

Comparative Polymer C-4 (“Urethane Acrylate (b)” in the publication) was synthesized according to paragraph 0184 of JP2013-199602A.

578.0 parts of a trimer (CORONATE (Registered trademark) HXR, manufactured by Tosoh Corporation) of hexamethylene diisocyanate (HDI), 200.0 parts of methoxy PEG400 (methoxy polyethylene glycol, manufactured by Toho Chemical Industry Co., Ltd.), and 200.0 parts of methoxy PEG1000 were introduced to a reaction vessel including a stirrer, a cooling pipe, a dropping funnel, and an air introduction pipe, 0.39 parts of stannous octoate was added under stirring, and the temperature in the reaction vessel was increased to 75° C., so as to perform reaction for 1.5 hours. Subsequently, 1051.6 parts of pentaerythritol triacrylate, 1.01 parts of methoquinone, and 0.81 parts of stannous octoate were introduced to this reaction vessel and were mixed with each other, the temperature in the reaction vessel under air bubbling was increased to 80° C., reaction was performed for two hours, and cooling was performed, so as to obtain Comparative Polymer C-4 (Urethane Acrylate (b)).

Comparative Polymer C-4 (Urethane Acrylate (b)) was urethane acrylate of which one terminal was an acryloyl group and in which trifunctional isocyanate was used.

Weight-average molecular weights (Mw) of the isocyanate group-containing polymers and the comparative polymers synthesized above are as provided in Table 1.

In the present example, a weight-average molecular weight (Mw) was measured in terms of polystyrene, by gel permeation chromatography (GPC). Used columns were TSKgel (Registered trademark) SuperHZM-H, TSKgel (Registered trademark) SuperHZ4000, and TSKgel (Registered trademark) SuperHZ200 (above are all manufactured by Tosoh Corporation).

Hereinafter, for the convenience of description, each of the examples and comparative examples is described with respect to Example 10.

Example 10

<Manufacturing of Water Dispersion>

(Emulsification Step)

—Manufacturing of Oil Phase Component—

An oil phase component was obtained by dissolving, 22.3 g of a solution (solid content 30 mass %) of Isocyanate Group-Containing Polymer P-10,

3.5 g of a 50 mass % ethyl acetate solution (manufactured by Mitsui Chemicals, Inc., TAKANATE (Registered trademark) D-116N; “116N” in Table 1) of an adduct (a compound having an ethyleneoxy group as a hydrophilic group) of trimethylolpropane, xylene diisocyanate, and polyethylene glycol monomethyl ether,

7 g of SR-399E (dipentaerythritol pentaacrylate; manufactured by Sartomer; “399E” in Table 1) as a polymerizable monomer, and

1.07 g of IRGACURE (Registered trademark) 819 (manufactured by BASF SE; “IRG819” in Table 1) as a photopolymerization initiator, in 16 g of ethyl acetate,

—Manufacturing of Water Phase Component—

A water phase component was obtained by dissolving 0.493 g of sodium hexadecyl sulfate (SCS) as a compound having a hydrophilic group (sodium salt of sulfate group) in 46 g of distilled water.

The mixture obtained by mixing the oil phase component and the water phase component was emulsified for 10 minutes at 12,000 rpm by using a homogenizer.

(Gelation Step)

A water dispersion of gel particles was obtained by heating the emulsion and reacting Isocyanate Group-Containing Polymer P-10 (referred to as “Raw material” in Table 1) and water. In this reaction, an isocyanate group of Isocyanate Group-Containing Polymer P-10 and water were reacted with each other, so as to form a three-dimensional crosslinked structure (Structure (S-10)) having a urea bond. Detailed operations are provided below.

Ethyl acetate and methyl ethyl ketone were distilled from the emulsion by adding 16.3 g of distilled water to the emulsion and subsequently performing heating at 40° C. for 5 hours under stirring. The temperature of the obtained liquid was increased to 50° C., the liquid was stirred at 50° C. for 24 hours, so as to form particles in the liquid. The liquid including particles was diluted with distilled water such that the solid content (that is, content of particles) become 20 mass %, so as to obtain a water dispersion of the particles.

<Determination of Gelling>

The following operations were performed in the condition of the liquid temperature of 25° C.

Samples were gathered from the water dispersion. With respect to the gathered samples, 100 times by mass of tetrahydrofuran (THF) were added and mixed with respect to the total solid content of the sample (particles in the present example) so as to prepare a diluent of the water dispersion. With respect to the obtained diluent, centrifugation was performed under the conditions of 80,000 rpm and 40 minutes. After the centrifugation, whether there are residues was visually checked. In a case where there were residues, water was added to these residues, stirring was performed for one hour with a stirrer, such that the residues were re-dispersed with water, so as to obtain a redispersion liquid. A particle size distribution of the obtained redispersion liquid was measured by a light scattering method by using a wet-type particle size distribution determination device (LA-910, manufactured by Horiba Ltd.).

Whether particles were gelled (that is, whether particles are gel particles) was determined according to the following determination standard based on the results of the operations.

The results are provided in Table 1.

—Determination Standard of Gelling—

Y: Residues were checked after centrifugation, particle size distribution of the redispersion liquid was checked, and it was checked that particles were gelled (that is, particles were gel particles).

N: Residues were not checked after centrifugation, or particle size distribution of the redispersion liquid was not checked even in a case where residues were checked, and gelling was not checked.

<Measuring of Volume Average Particle Diameter of Gel Particles>

A volume average particle diameter (hereinafter, simply referred to as “particle diameter”) of the obtained gel particles in the water dispersion was measured by a light scattering method by using LA-910.

The results are provided in Table 1.

<Manufacturing of Ink Composition>

The following components were mixed, so as to manufacture an ink composition.

The obtained ink composition is an aspect of the water dispersion of gel particles.

—Components of Ink Composition—

-   -   The above water dispersion . . . 82 parts     -   Pigment dispersion liquid (Pro-jet Cyan APD1000 (Registered         trademark) (manufactured by FUJIFILM Imaging Colorants, Inc.) .         . . 13 parts     -   Fluorine-based surfactant (manufactured by DuPont, Zonyl FS300)         . . . 0.7 parts     -   2-Methylpropanediol . . . 4.3 parts

<Evaluation>

The following evaluation was performed by using the ink composition which is an aspect of the water dispersion of gel particles.

The results are provided in Table 2.

(Adhesiveness of Cured Film (Cross Hatch Test))

The adhesiveness was evaluated by using each of the evaluation sample (PVC), the evaluation samples (PS), the evaluation samples (PC), the evaluation samples (PET), the evaluation samples (G-modified PET), the evaluation samples (PP), and the evaluation samples (Acryl).

An evaluation sample (PVC) was manufactured by coating a polyvinyl chloride (PVC) sheet as a base material with the ink composition obtained above in a thickness of 12 μm by using bar No. 2 of K hand coater manufactured by RK PRINT COAT INSTRUMENTS Ltd. and heating and drying the obtained coated film at 60° C. for three minutes.

The evaluation sample (PS) was manufactured in the same manner as the manufacturing of the evaluation sample (PVC) except for changing the base material to a polystyrene (PS) sheet.

The evaluation sample (PC) was manufactured in the same manner as the manufacturing of the evaluation sample (PVC) except for changing the base material to a polycarbonate (PC) sheet.

The evaluation sample (PET) was manufactured in the same manner as the manufacturing of the evaluation sample (PVC) except for changing the base material to a polyethylene terephthalate (PET) sheet.

The evaluation sample (G-modified PET) was manufactured in the same manner as the manufacturing of the evaluation sample (PVC) except for changing the base material to a glycol-modified polyethylene terephthalate (G-modified PET) sheet.

The evaluation sample (PP) was manufactured in the same manner as the manufacturing of the evaluation sample (PVC) except for changing the base material to a polypropylene (PP) sheet.

The evaluation sample (Acryl) was manufactured in the same manner as the manufacturing of the evaluation sample (PVC) except for changing the base material to an acrylic resin sheet.

Here, the following sheets were used for each of the PVC sheet, the PS sheet, the PC sheet, the PET sheet, the PP sheet, the G-modified PET sheet, and the acrylic resin sheet.

PVC sheet: “AVERY (Registered trademark) 400 GLOSS WHITE PERMANENT” manufactured by Avery Dennison Corporation

PS sheet: “falcon hi impact polystyrene” manufactured by Robert Horne Group Ltd.

PC sheet: “PC1600-2” manufactured by Takiron Co., Ltd.

PP sheet: “Correx” manufactured by Robert Horne Group Ltd.

PET sheet: PET sheet manufactured by Robert Horne Group Ltd.

G-modified PET sheet: “VIVAK (Registered trademark)” manufactured by Bayer AG

Acrylic resin sheet: “ACRYACE (Registered trademark) UV” manufactured by JSP Corporation

In the evaluation of the adhesiveness, a UV mini conveyor device for a test CSOT (manufactured by GS Yuasa International Ltd.) to which an ozone-less metal halide lamp MAN250L was mounted as an exposure device and in which a conveyor speed was set as 35 m/min and exposure intensity was set as 2.0 W/cm² was used.

With respect to the coated film of each evaluation sample, the coated film was cured by irradiating the coated film with the UV light (ultraviolet rays) using the exposure device, so as to obtain a cured film.

A cross hatch test was performed on the cured film in conformity with ISO2409 (cross cut method) and the cured film was evaluated according to the following evaluation standard.

In this cross hatch test, cut intervals were set to 1 mm, and 25 square lattices having angles of 1 mm were formed.

According to the following evaluation standard, 0 and 1 are levels that are acceptable in practice.

According to the evaluation standard, a proportion (%) in which a lattice was peeled off was a value obtained by the following equation. The total number of the lattices according to the following equation was 25. Ratio of peeled lattice (%)=[(the number of lattices in which peeling was generated)/(the total number of lattices)]×100

—Evaluation Standard of Adhesiveness of Cured Film—

0: A proportion (%) in which a lattice was peeled off was 0%.

1: A proportion (%) in which a lattice was peeled off was greater than 0% and 5% or less.

2: A proportion (%) in which a lattice was peeled off was greater than 5% and 15% or less.

3: A proportion (%) in which a lattice was peeled off was greater than 15% and 35% or less.

4: A proportion (%) in which a lattice was peeled off was greater than 35% and 65% or less.

5: A proportion (%) in which a lattice was peeled off was greater than 65%.

(Pencil Hardness of Cured Film)

Pencil hardness of the cured film was evaluated by using the above evaluation sample (PVC).

In the same manner as the evaluation of the adhesiveness of the cured film, the coated film of the evaluation sample (PVC) was irradiated with UV light and was cured, so as to obtain a cured film.

A pencil hardness test was performed on a cured film in conformity with JIS K5600-5-4 (1999) by using UNI (Registered trademark) manufactured by Mitsubishi Pencil Co., Ltd. as a pencil.

According to the test results, an allowable range of the pencil hardness is HB or harder and preferably H or harder. A printed matter having the pencil hardness of B or less is not preferable, since there is a possibility that scratches may be generated in a case of handling the printed matter.

(Jettability of Ink Composition)

The ink composition obtained above was ejected from the head of an ink jet printer (SP-300V, manufactured by Roland DG Corporation) for 30 minutes and then the ejection was stopped.

After five minutes had elapsed from the stop of the ejection, the ink composition was ejected to the polyvinyl chloride (PVC) sheet described above from the head, so as to form a solid image of 5 cm×5 cm.

These images were visually observed so as to check existence of dot losses due to the generation of the non-ejection nozzles, and jettability of the ink composition was evaluated according to the following evaluation standard.

In the following evaluation standards, jettability of an ink composition was most excellent in A.

—Evaluation Standard of Jettability of Ink Composition—

A: Dot losses were not acknowledged due to the generation of the non-ejection nozzles and the like, and a satisfactory image was able to be obtained.

B: Some dot losses due to the generation of the non-ejection nozzles and the like were acknowledged, but no troubles were generated in practice.

C: Dot losses due to the generation of the non-ejection nozzles and the like were generated, but an image was unsatisfactory in practice.

D: Ejection from heads was not able to be performed.

(Redispersibility of Ink Composition)

The following operation was performed under a yellow lamp so as to evaluate redispersibility of the ink compositions.

An aluminum plate was coated with the ink composition in a thickness of 12 μm by using bar No. 2 of K hand coater manufactured by RK PRINT COAT INSTRUMENTS Ltd, so as to form a coated film. The obtained coated film was dried by heating at 60° C. for 3 minutes. The surface of the coated film after being dried was rubbed with a sponge impregnated with water.

Fourier transform infrared spectroscopy (FT-IR) was performed on each of the coated films before being rubbed with a sponge and the coated film after being rubbed. Residual ratios of gel particles were calculated based on the following equation from obtained results. Residual ratio of gel particles=(Intensity of peak derived from gel particles in coated film after being rubbed with sponge/Intensity of peak derived from gel particles in coated film before being rubbed with sponge)×100

Here, a peak derived from gel particles means a peak derived from an urea bond.

—Evaluation Standard of Redispersibility of Ink Composition—

A: A residual ratio of the gel particles was 1% or less, and redispersibility was excellent.

B: A residual ratio of the gel particles was greater than 1% and 5% or less, and redispersibility was in a range acceptable in practice.

C: A residual ratio of the gel particles was greater than 5% and 10% or less, and redispersibility was out of a range acceptable in practice.

D: A residual ratio of the gel particles was greater than 10%, and redispersibility was extremely bad.

(Preservation Stability of Ink Composition)

The ink compositions were sealed in a container, two weeks had elapsed at 60° C., the same evaluation as the above jettability evaluation was performed, and preservation stability of the ink composition was evaluated according to the same evaluation standard.

In the evaluation standards, preservation stability of an ink composition was most excellent in A.

Examples 1 to 9 and 11 to 64, Comparative Examples 1 and 2

The same operation was performed in the same manner as in Example 10 except for changing the followings. The results are provided in Tables 1 and 2.

—Changes from Example 10—

In all examples, combinations of a kind (Section “Raw material” in Table 1) of an isocyanate group-containing polymer used as a raw material of a three-dimensional crosslinked structure, a kind of a compound having a hydrophilic group, a kind of a polymerizable monomer, and a kind of a photopolymerization initiator were changed as presented in Table 1.

In examples in which 116N was not provided (for example, Examples 33 to 45), TAKANATE D-116N, an ethyl acetate 50% solution was not used in an oil phase component, an amount (22.3 g in Example 10) of the solution of the isocyanate group-containing polymer was changed to 28.14 g, and an amount (16 g in Example 10) of ethyl acetate in the oil phase component was changed to 13 g.

In an example (for example, Example 33 (Structure (S-33))) in which a —COONa group was included as a hydrophilic group in a three-dimensional crosslinked structure, 0.353 g of sodium hydroxide was further contained in the water phase component.

In an example (for example, Example 36 (Structure (S-36))) in which a —SO₃Na group was included as a hydrophilic group in a three-dimensional crosslinked structure, 0.147 g of sodium hydroxide was further contained in the water phase component.

In Examples 37 to 39, sodium hexadecyl sulfate (SCS) was changed to sodium dodecyl sulfate (SDS) in the same mass.

In Example 45, 399E (polymerizable monomer) was not contained in the oil phase component. In this Example 45, Structure (S-44) has a polymerizable group (acryloyl group).

In Examples 46 to 51, a polymerizable monomer (399E in Example 10) was changed to each of compounds provided in Table 1.

In Examples 54 to 64, 0.3 g of a sensitizer presented in Table 1 was further contained in the oil phase component.

Comparative Examples 3 to 4

With reference to paragraphs 0187 and 0188 disclosed in JP2013-199602A, emulsions for comparison (emulsions for comparison) with the water dispersions of the above respective examples were manufactured. Details thereof are provided below.

27.5 parts of a comparative polymer (Comparative Polymer 3 or 4), 9.2 parts of tripentaerythritol polyacrylate (VISCOAT #802 manufactured by Osaka Organic Chemical Industry Ltd.), and 3.3 parts of a photoradical polymerization initiator (TPO) were introduced to a reaction vessel including a stirrer, a cooling pipe, a dropping funnel, and an air introduction pipe, the temperature in the reaction vessel was increased to 80° C. under stirring, and the temperature was maintained for two hours.

Subsequently, after the temperature in the reaction vessel was cooled down to 50° C., 60 parts of deionized water was added under stirring, and the temperature was maintained for one hour at 40° C., so as to obtain a dispersion liquid of 40 mass % of a nonvolatile content (comparative polymer, tripentaerythritol polyacrylate, and a polyradical polymerization initiator (TPO)). Distilled water was added to obtained dispersion liquid, so as to obtain an emulsion for comparison having a solid content of 20 mass %.

The same operation as in Example 10 was performed except for changing a water dispersion in Example 10, to the same mass of an emulsion for comparison.

The results are presented in Tables 1 and 2.

TABLE 1 Particles Three-dimensional crosslinked structure Raw material Unit C(O) Urea Hydrophilic Polymerizable Gelling Kind Mw Structure (1) X2R2 bond group group Example 1 Y P-1 30000 S-1 Y N Y N N Example 2 Y P-2 35000 S-2 Y N Y N N Example 3 Y P-3 25000 S-3 Y N Y N N Example 4 Y P-4 25000 S-4 Y N Y N N Example 5 Y P-5 30000 S-5 Y N Y N N Example 6 Y P-6 30000 S-6 Y N Y N N Example 7 Y P-7 10000 S-7 Y N Y N N Example 8 Y P-8 15000 S-8 Y N Y N N Example 9 Y P-9 15000 S-9 Y N Y N N Example 10 Y P-10 35000 S-10 Y Y Y N N Example 11 Y P-11 35000 S-11 Y Y Y N N Example 12 Y P-12 35000 S-12 Y Y Y N N Example 13 Y P-13 35000 S-13 Y Y Y N N Example 14 Y P-14 35000 S-14 Y Y Y N N Example 15 Y P-15 35000 S-15 Y Y Y N N Example 16 Y P-16 40000 S-16 Y Y Y N N Example 17 Y P-17 35000 S-17 Y Y Y N N Example 18 Y P-18 35000 S-18 Y Y Y N N Example 19 Y P-19 40000 S-19 Y Y Y N N Example 20 Y P-20 35000 S-20 Y Y Y N N Example 21 Y P-21 35000 S-21 Y Y Y N N Example 22 Y P-22 35000 S-22 Y Y Y N N Example 23 Y P-23 35000 S-23 Y Y Y N N Example 24 Y P-24 35000 S-24 Y Y Y N N Example 25 Y P-25 35000 S-25 Y Y Y N N Example 26 Y P-26 40000 S-26 Y Y Y N N Example 27 Y P-27 35000 S-27 Y Y Y N N Example 28 Y P-28 15000 S-28 Y Y Y N N Example 29 Y P-29 20000 S-29 Y Y Y N N Example 30 Y P-30 20000 S-30 Y Y Y N N Example 31 Y P-31 40000 S-31 Y Y Y N N Example 32 Y P-32 40000 S-32 Y Y Y N N Example 33 Y P-33 30000 S-33 Y N Y Y N Example 34 Y P-34 35000 S-34 Y Y Y Y N Example 35 Y P-35 35000 S-35 Y Y Y Y N Example 36 Y P-36 35000 S-36 Y Y Y Y N Example 37 Y P-34 35000 S-34 Y Y Y Y N Example 38 Y P-37 40000 S-37 Y Y Y Y N Example 39 Y P-38 40000 S-38 Y Y Y Y N Example 40 Y P-39 15000 S-39 Y Y Y Y N Example 41 Y P-40 20000 S-40 Y Y Y Y N Example 42 Y P-41 20000 S-41 Y Y Y Y N Example 43 Y P-42 40000 S-42 Y Y Y Y N Example 44 Y P-43 40000 S-43 Y Y Y Y N Example 45 Y P-44 35000 S-44 Y Y Y N Y Example 46 Y P-10 35000 S-10 Y Y Y N N Example 47 Y P-10 35000 S-10 Y Y Y N N Example 48 Y P-10 35000 S-10 Y Y Y N N Example 49 Y P-39 15000 S-39 Y Y Y Y N Example 50 Y P-40 20000 S-40 Y Y Y Y N Example 51 Y P-41 20000 S-41 Y Y Y Y N Example 52 Y P-10 35000 S-10 Y Y Y N N Example 53 Y P-10 35000 S-10 Y Y Y N N Example 54 Y P-10 35000 S-10 Y Y Y N N Example 55 Y P-10 35000 S-10 Y Y Y N N Example 56 Y P-10 35000 S-10 Y Y Y N N Example 57 Y P-15 35000 S-15 Y Y Y N N Example 58 Y P-17 35000 S-17 Y Y Y N N Example 59 Y P-18 35000 S-18 Y Y Y N N Example 60 Y P-34 35000 S-34 Y Y Y Y N Example 61 Y P-35 35000 S-35 Y Y Y Y N Example 62 Y P-39 15000 S-39 Y Y Y Y N Example 63 Y P-40 20000 S-40 Y Y Y Y N Example 64 Y P-41 20000 S-41 Y Y Y Y N Comparative N C-1 40000 — Y Y N Y N Example 1 Comparative N C-2 35000 — Y Y N Y N Example 2 Comparative N C-3 N.D. — N N N Y N Example 3 Comparative N C-4 N.D. — N N N Y N Example 4 Particles Polymerizable monomer Compound The having number Particle hydrophilic of photopolymerization diameter group Kind functions initiator Sensitizer (μm) Example 1 SCS 116N 399E 5 IRG819 — 0.15 Example 2 SCS 116N 399E 5 IRG819 — 0.15 Example 3 SCS 116N 399E 5 IRG819 — 0.15 Example 4 SCS 116N 399E 5 IRG819 — 0.15 Example 5 SCS 116N 399E 5 IRG819 — 0.15 Example 6 SCS 116N 399E 5 IRG819 — 0.15 Example 7 SCS 116N 399E 5 IRG819 — 0.15 Example 8 SCS 116N 399E 5 IRG819 — 0.15 Example 9 SCS 116N 399E 5 IRG819 — 0.15 Example 10 SCS 116N 399E 5 IRG819 — 0.15 Example 11 SCS 116N 399E 5 IRG819 — 0.15 Example 12 SCS 116N 399E 5 IRG819 — 0.15 Example 13 SCS 116N 399E 5 IRG819 — 0.15 Example 14 SCS 116N 399E 5 IRG819 — 0.15 Example 15 SCS 116N 399E 5 IRG819 — 0.15 Example 16 SCS 116N 399E 5 IRG819 — 0.15 Example 17 SCS 116N 399E 5 IRG819 — 0.15 Example 18 SCS 116N 399E 5 IRG819 — 0.15 Example 19 SCS 116N 399E 5 IRG819 — 0.15 Example 20 SCS 116N 399E 5 IRG819 — 0.15 Example 21 SCS 116N 399E 5 IRG819 — 0.15 Example 22 SCS 116N 399E 5 IRG819 — 0.15 Example 23 SCS 116N 399E 5 IRG819 — 0.15 Example 24 SCS 116N 399E 5 IRG819 — 0.15 Example 25 SCS 116N 399E 5 IRG819 — 0.15 Example 26 SCS 116N 399E 5 IRG819 — 0.15 Example 27 SCS 116N 399E 5 IRG819 — 0.15 Example 28 SCS 116N 399E 5 IRG819 — 0.15 Example 29 SCS 116N 399E 5 IRG819 — 0.15 Example 30 SCS 116N 399E 5 IRG819 — 0.15 Example 31 SCS 116N 399E 5 IRG819 — 0.15 Example 32 SCS 116N 399E 5 IRG819 — 0.15 Example 33 SCS — 399E 5 IRG819 — 0.18 Example 34 SCS — 399E 5 IRG819 — 0.18 Example 35 SCS — 399E 5 IRG819 — 0.15 Example 36 SCS — 399E 5 IRG819 — 0.16 Example 37 SDS — 399E 5 IRG819 — 0.18 Example 38 SDS — 399E 5 IRG819 — 0.18 Example 39 SDS — 399E 5 IRG819 — 0.18 Example 40 SCS — 399E 5 IRG819 — 0.15 Example 41 SCS — 399E 5 IRG819 — 0.18 Example 42 SCS — 399E 5 IRG819 — 0.18 Example 43 SCS — 399E 5 IRG819 — 0.18 Example 44 SCS — 399E 5 IRG819 — 0.15 Example 45 SCS 116N — — IRG819 — 0.15 Example 46 SCS 116N DA1 2 IRG819 — 0.15 Example 47 SCS 116N TMM3L 3 IRG819 — 0.15 Example 48 SCS 116N DPH 6 IRG819 — 0.15 Example 49 SCS — DA1 2 IRG819 — 0.15 Example 50 SCS — TMM3L 3 IRG819 — 0.18 Example 51 SCS — DPH 6 IRG819 — 0.18 Example 52 SCS 116N 399E 5 IRG907 — 0.15 Example 53 SCS 116N 399E 5 TPO — 0.15 Example 54 SCS 116N 399E 5 IRG819 1331 0.15 Example 55 SCS 116N 399E 5 IRG819 ITX 0.15 Example 56 SCS 116N 399E 5 IRG819 DETX 0.15 Example 57 SCS 116N 399E 5 IRG819 ITX 0.15 Example 58 SCS 116N 399E 5 IRG819 ITX 0.15 Example 59 SCS 116N 399E 5 IRG819 ITX 0.15 Example 60 SCS — 399E 5 IRG819 ITX 0.18 Example 61 SCS — 399E 5 IRG819 ITX 0.15 Example 62 SCS — 399E 5 IRG819 ITX 0.15 Example 63 SCS — 399E 5 IRG819 ITX 0.18 Example 64 SCS — 399E 5 IRG819 ITX 0.18 Comparative SCS — 399E 5 IRG819 — 0.20 Example 1 Comparative SCS — 399E 5 IRG819 — 0.18 Example 2 Comparative — — #802 8 TPO — 0.30 Example 3 Comparative — — #802 8 TPO — 0.30 Example 4

TABLE 2 Evaluation results (Ink composition) Pencil Preservation Adhesiveness hardness Jettability Redispersibility stability PVC PS PC PET G-modified PET PP Acryl Example 1 H A A B 0 1 1 1 1 1 1 Example 2 H A A B 0 1 1 1 1 1 1 Example 3 H A A B 0 0 1 1 1 1 1 Example 4 H A A B 0 0 1 1 1 1 1 Example 5 2H A A B 0 0 1 1 1 1 1 Example 6 H A A B 0 0 1 1 1 1 1 Example 7 H A A B 0 1 1 0 1 1 1 Example 8 H A A B 0 1 1 0 1 1 1 Example 9 H A A B 0 0 1 0 1 1 1 Example 10 H A A B 0 0 0 0 0 1 0 Example 11 H A A B 0 0 0 0 1 1 0 Example 12 2H A A B 0 0 0 0 0 1 0 Example 13 F A A B 0 0 0 0 0 1 0 Example 14 2H A A B 0 0 0 0 1 1 0 Example 15 H A A B 0 0 0 0 0 1 0 Example 16 2H A A B 0 0 0 0 0 1 0 Example 17 F A A B 0 0 0 0 1 1 1 Example 18 H A A B 0 0 0 0 1 1 1 Example 19 H A A B 0 0 0 0 1 1 1 Example 20 F A A B 0 0 0 0 1 1 1 Example 21 H A A B 0 0 0 0 1 1 1 Example 22 H A A B 0 0 0 0 1 1 1 Example 23 H A A B 0 0 0 0 1 1 1 Example 24 H A A B 0 0 0 0 0 1 1 Example 25 H A A B 0 0 0 0 0 1 1 Example 26 H A A B 0 0 0 0 0 1 1 Example 27 H A A B 0 0 0 0 0 1 1 Example 28 H A A B 0 0 0 0 0 1 0 Example 29 2H A A B 0 0 0 0 0 1 0 Example 30 H A A B 0 0 0 0 0 1 1 Example 31 H A A B 0 0 0 0 0 1 0 Example 32 F A A B 0 0 0 0 0 1 0 Example 33 H A A A 0 1 1 1 1 1 1 Example 34 H A A A 0 0 0 0 0 1 0 Example 35 H A A A 0 0 0 0 0 1 0 Example 36 H A A A 0 0 0 0 0 1 0 Example 37 H A A A 0 0 0 0 0 1 0 Example 38 2H A A A 0 0 0 0 0 1 0 Example 39 H A A A 0 0 0 0 0 1 1 Example 40 H A A A 0 0 0 0 0 1 0 Example 41 2H A A A 0 0 0 0 0 1 0 Example 42 H A A A 0 0 0 0 0 1 1 Example 43 H A A A 0 0 0 0 0 1 0 Example 44 H A A A 0 0 0 0 0 1 0 Example 45 H A A B 0 0 0 0 0 1 1 Example 46 HB A A B 0 0 0 0 1 1 1 Example 47 H A A B 0 0 0 0 0 1 0 Example 48 H A A B 0 0 0 0 0 1 0 Example 49 HB A A A 0 0 0 0 1 1 1 Example 50 H A A A 0 0 0 0 0 1 0 Example 51 H A A A 0 0 0 0 0 1 0 Example 52 F A A B 0 0 0 0 0 1 1 Example 53 H A A B 0 0 0 0 0 1 0 Example 54 H A A B 0 0 0 0 0 1 0 Example 55 2H A A B 0 0 0 0 0 1 0 Example 56 2H A A B 0 0 0 0 0 1 0 Example 57 2H A A B 0 0 0 0 0 1 0 Example 58 H A A B 0 0 0 0 0 1 1 Example 59 2H A A B 0 0 0 0 0 1 1 Example 60 2H A A A 0 0 0 0 0 1 0 Example 61 2H A A A 0 0 0 0 0 1 0 Example 62 2H A A A 0 0 0 0 0 1 0 Example 63 3H A A A 0 0 0 0 0 1 0 Example 64 2H A A A 0 0 0 0 0 1 1 Comparative <3B D D D 3 4 5 4 5 5 5 Example 1 Comparative <3B D D D 4 5 5 5 5 5 5 Example 2 Comparative <3B D D D 5 5 5 5 5 5 5 Example 3 Comparative <3B D D D 5 5 5 5 5 5 5 Example 4 —Descriptions of Table 1—

-   -   In Section “(1) unit” in Section “three-dimensional crosslinked         structure”, a case where a structural unit represented by         Formula (1) was included in the three-dimensional crosslinked         structure is presented as “Y”, and a case where a structural         unit was not included is presented as “N”.     -   In Section “C(O)X2R2” in Section “three-dimensional crosslinked         structure”, a case where X¹ in Formula (1) was a —C(═O)X²R²         group is presented as “Y”, and a case where X¹ in Formula (1)         was a group other than a —C(═O)X²R² group is presented as “N”.     -   In the same manner, in Section “urea bond”, Section “hydrophilic         group”, and Section “polymerizable group”, cases where these         bonds or groups were included in the three-dimensional         crosslinked structure are presented as “Y”, and cases where         these bonds or groups were not included are presented as “N”.     -   Polymerizable monomers are as provided below.

399E . . . SR-399E (dipentaerythritol pentaacrylate; pentafunctional polymerizable monomer) manufactured by Sartomer

DA1 . . . Diacrylate of neopentyl glycol propylene oxide adduct (NPGPODA; difunctional polymerizable monomer)

DPH . . . A-DPH (dipentaerythritol hexaacrylate; hexafunctional polymerizable monomer) manufactured by Shin-Nakamura Chemical Co., Ltd.

TMM3L . . . A-TMM-3L (Pentaerythritol triacrylate; trifunctional polymerizable monomer) manufactured by Shin-Nakamura Chemical Co., Ltd.

#802 . . . VISCOAT #802 (Polypentaerythritol polyacrylate; octafunctional polymerizable monomer) manufactured by Osaka Organic Chemical Industry Ltd.

-   -   Photopolymerization initiators are as follows.

IRG819 . . . IRGACURE (Registered trademark) 819 (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide; manufactured by BASF SE)

IRG907 . . . IRGACURE (Registered trademark) 907 (2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one; manufactured by BASF SE)

TPO . . . LUCIRIN (Registered trademark) TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide; manufactured by BASF SE)

-   -   Sensitizers are as follows.

1331 . . . Cationic photosensitizer ANTHRACURE (Registered trademark) UVS-1331 (9,10-Dibutoxyanthracene) manufactured by Kawasaki Kasei Chemicals Ltd.

ITX . . . 2-Isopropylthioxanthone

DETX . . . 2,4-Diethylthioxanthone

-   -   A compound having a hydrophilic group is as follows.

SCS . . . Sodium hexadecyl sulfate (compound having sodium salt of sulfate group as hydrophilic group)

SDS . . . Sodium dodecyl sulfate (compound having sodium salt of sulfate group as hydrophilic group)

116N . . . TAKANATE (Registered trademark) D-116N [50 mass % ethyl acetate solution of adduct of trimethylolpropane (TMP), xylene diisocyanate (XDI), and polyethylene glycol monomethyl ether (EO90) (compound having ethyleneoxy group as hydrophilic group; the structure is provided below)] manufactured by Mitsui Chemicals, Inc.

As presented in Tables 1 and 2, with the ink compositions (water dispersions of gel particles) of Example 1 to 64 in which gel particles having Structure (S-1) to (S-44) which were three-dimensional crosslinked structures including a structural unit represented by Formula (1) and a urea bond, having a hydrophilic group and a polymerizable group, and including a photopolymerization initiator were dispersed in water, it was possible to form images (that is, films) having excellent adhesiveness to various base materials and excellent pencil hardness. The ink compositions of Examples 1 to 64 were excellent in jettability, redispersibility, and preservation stability.

In contrast, in films formed by using ink compositions of Comparative Examples 1 to 4 not including gel particles (that is, particles were not gelled), adhesiveness to base materials and pencil hardness were decreased. In the ink compositions of Comparative Examples 1 to 4, jettability, redispersibility, and preservation stability were also deteriorated.

Among the examples, Examples 10 to 32 and 34 to 64, Section “C(O)X2R2” was “Y” (that is, X¹ in Formula (1) was a —C(═O)X²R² group) were particularly excellent in results of adhesiveness (see, for example, Section “PC” in Table 2).

Among the examples, Examples 33 to 44, 49 to 51, and 60 to 64 in which three-dimensional crosslinked structures included hydrophilic groups (Unit (W)) were particularly excellent in the results of preservation stability.

Among the examples, Examples 54 to 64 in which gel particles included sensitizers were particularly excellent in the results of pencil hardness.

In Examples 1 to 64, inclusion ratios (%) of the photopolymerization initiators in water dispersions (that is, water dispersions used as raw materials of ink compositions. the same is applied in the followings) before preparation of the ink compositions were measured by the above method. As a result, inclusion ratios (%) of the photopolymerization initiators were 99 mass % or greater.

In Examples 1 to 44 and 46 to 64, inclusion ratios (%) of the polymerizable monomers in the water dispersions before the preparation of the ink compositions were measured by the above method. As a result, inclusion ratios (%) of the polymerizable monomers were 99 mass % or greater.

In Examples 54 to 64, inclusion ratios (%) of the sensitizers in the water dispersions before preparation of the ink compositions were measured by the above method. As a result, inclusion ratios (%) of the sensitizers were 99 mass % or greater.

According to the results of the Fourier transform infrared spectroscopy (FT-IR) analysis, all of the gel particles in the water dispersions (specifically, the water dispersions before preparation of the ink compositions) in Examples 1 to 64 were gel particles having a polymerizable group.

<Evaluation Using LED>

The respective ink compositions manufactured in Examples 3, 10, 34, 35, 40 to 42, and 54 to 64 were evaluated by using an LED.

Specifically, in the evaluation of pencil hardness and the adhesiveness in the respective examples, the same operations were performed except for changing a UV light source to a 385 nmUV-LED irradiator (manufactured by CCS Inc.) for a test and changing the exposure energies to 300 mJ/cm².

Results are provided in Table 3.

TABLE 3 Evaluation results (Ink composition, LED light: 385 nm) Adhesiveness G- Pencil modified hardness PVC PS PC PET PET PP Acryl Example 3 H 0 1 1 1 1 1 1 Example 10 H 0 0 0 0 0 1 0 Example 34 H 0 0 0 0 0 1 0 Example 35 H 0 0 0 0 0 1 0 Example 40 H 0 0 0 0 0 1 0 Example 41 2H 0 0 0 0 0 1 0 Example 42 H 0 0 0 0 0 1 1 Example 54 H 0 0 0 0 0 1 0 Example 55 2H 0 0 0 0 0 1 0 Example 56 2H 0 0 0 0 0 1 0 Example 57 2H 0 0 0 0 0 1 0 Example 58 H 0 0 0 0 0 1 1 Example 59 2H 0 0 0 0 0 1 1 Example 60 2H 0 0 0 0 0 1 0 Example 61 2H 0 0 0 0 0 1 0 Example 62 2H 0 0 0 0 0 1 0 Example 63 3H 0 0 0 0 0 1 0 Example 64 2H 0 0 0 0 0 1 1

As presented in Table 3, in the ink compositions of these examples, even in the evaluation of the pencil hardness and the adhesiveness using LED light, excellent results were able to be obtained.

<Evaluation of Coating Solution>

Coating solutions were manufactured by using the water dispersions manufactured in Examples 1 to 64 and Comparative Examples 1 to 4, evaluations of pencil hardness and adhesiveness (PVC and Acryl) were performed by the above methods by using the manufactured coating solutions. The results are provided in Table 4.

—Components of Coating Solution—

-   -   Above water dispersion . . . 82 parts     -   Fluorine-based surfactant (Zonyl FS300 manufactured by DuPont) .         . . 0.7 parts     -   2-Methylpropanediol . . . 4.3 parts     -   Water . . . The rest portion that makes 100 parts as a whole

TABLE 4 Evaluation results (Coating Solution) Adhesiveness Pencil hardness PVC Acryl Example 1 H 0 1 Example 2 H 0 1 Example 3 H 0 1 Example 4 H 0 1 Example 5 2H 0 1 Example 6 H 0 1 Example 7 H 0 1 Example 8 H 0 1 Example 9 H 0 1 Example 10 H 0 0 Example 11 H 0 0 Example 12 2H 0 0 Example 13 F 0 0 Example 14 2H 0 0 Example 15 H 0 0 Example 16 2H 0 0 Example 17 F 0 1 Example 18 H 0 1 Example 19 H 0 1 Example 20 F 0 1 Example 21 H 0 1 Example 22 H 0 1 Example 23 H 0 1 Example 24 H 0 1 Example 25 H 0 1 Example 26 H 0 1 Example 27 H 0 1 Example 28 H 0 0 Example 29 2H 0 0 Example 30 H 0 1 Example 31 H 0 0 Example 32 F 0 0 Example 33 H 0 1 Example 34 H 0 0 Example 35 H 0 0 Example 36 H 0 0 Example 37 H 0 0 Example 38 2H 0 0 Example 39 H 0 1 Example 40 H 0 0 Example 41 2H 0 0 Example 42 H 0 1 Example 43 H 0 0 Example 44 H 0 0 Example 45 H 0 1 Example 46 HB 0 1 Example 47 H 0 0 Example 48 H 0 0 Example 49 HB 0 1 Example 50 H 0 0 Example 51 H 0 0 Example 52 F 0 1 Example 53 H 0 0 Example 54 H 0 0 Example 55 2H 0 0 Example 56 2H 0 0 Example 57 2H 0 0 Example 58 H 0 1 Example 59 2H 0 1 Example 60 2H 0 0 Example 61 2H 0 0 Example 62 2H 0 0 Example 63 3H 0 0 Example 64 2H 0 1 Comparative Example 1 <3B  3 5 Comparative Example 2 <3B  4 5 Comparative Example 3 <3B  5 5 Comparative Example 4 <3B  5 5

As presented in Table 4, it was possible to form images (that is, films) having excellent adhesiveness to various base materials and excellent pencil hardness with the water dispersions of gel particles of Example 1 to 64.

In contrast, adhesiveness to base materials and pencil hardness were decreased films formed by coating solutions using ink compositions of Comparative Examples 1 to 4 not including gel particles (that is, particles were not gelled).

The whole of the disclosure of Japanese Patent Application No. 2015-061718 filed on Mar. 24, 2015 is incorporated into the present specification by reference.

All the documents, patent applications, and technical standards described in the present specification are incorporated into the present specification by reference to the same extent as that in the case where it is specifically and individually shown that each of the documents, patent applications, and technical standards is incorporated into the present specification by reference. 

What is claimed is:
 1. A water dispersion of gel particles, wherein the gel particles have a three-dimensional crosslinked structure including a structural unit represented by Formula (1) and a urea bond, have a hydrophilic group, include photopolymerization initiators and are dispersed in water,

R¹ in Formula (1) represents a hydrogen atom or an alkyl group, X¹ in Formula (1) represents a cyano group, a lactam group, a —C(═O)X²R² group, an —OC(═O)R³ group, or an aryl group, X² represents an oxygen atom or an —N(R^(X2))— group, and R^(X2) represents a hydrocarbon group that may contain a hetero atom or a hydrogen atom, R² represents a hydrocarbon group that may contain a hetero atom or a hydrogen atom, provided that, in a case in which X² is an oxygen atom, R² is not a hydrogen atom, R² and R^(X2) may be bonded to each other to form a ring, R³ represents a hydrocarbon group that may contain a hetero atom, and a content of the structural unit represented by Formula (1) in the three-dimensional crosslinked structure is 60 mass % or greater with respect to a total amount of the three-dimensional crosslinked structure.
 2. The water dispersion of gel particles according to claim 1, wherein, in Formula (1), R¹ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, X¹ is a cyano group, a lactam group, a —C(═O)X²R² group, an —OC(═O)R³ group, or an aryl group, X² is an oxygen atom or an —N(R^(X2))— group, R^(X2) is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, R² is a hydrogen atom, an alkyl group having 1 to 30 carbon atoms, an alkoxyalkyl group having 2 to 30 carbon atoms, a polyalkoxyalkyl group having 3 to 30 carbon atoms, an aryloxyalkyl group having 7 to 30 carbon atoms, an aminoalkyl group having 1 to 30 carbon atoms, a monoalkylaminoalkyl group having 2 to 30 carbon atoms, or a dialkylaminoalkyl group having 3 to 30 carbon atoms, and R³ is an alkyl group having 1 to 6 carbon atoms.
 3. The water dispersion of gel particles according to claim 1, wherein X¹ in Formula (1) is a —C(═O)X²R² group.
 4. The water dispersion of gel particles according to claim 1, wherein the three-dimensional crosslinked structure includes at least one of a structural unit represented by Formula (2) or a group represented by Formula (3),

R²¹ in Formula (2) represents a hydrogen atom or an alkyl group, L²¹ in Formula (2) represents a divalent hydrocarbon group that may contain a hetero atom, X²¹ in Formula (2) represents an oxygen atom or a —C(═O)X²²L²²O— group, X²² represents an oxygen atom or a —N(R^(x22))— group, R^(x22) represents a hydrocarbon group that may contain a hetero atom, L²² represents a divalent hydrocarbon group that may contain a hetero atom, in Formula (2), p represents 0 or 1, in Formula (3), Z³¹ represents a (n+1)-valent organic group and Z³² represents a (m+1)-valent organic group, n in Formula (3) represents an integer of 1 to 4 and m represents an integer of 1 to 4, and in Formulae (2) and (3), * represents a bonding position.
 5. The water dispersion of gel particles according to claim 4, wherein, in Formula (2), R²¹ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, L²¹ is an alkylene group having 1 to 30 carbon atoms, an arylene group having 6 to 30 carbon atoms, an alkylene arylene group having 7 to 30 carbon atoms, an alkylene arylene alkylene group having 8 to 30 carbon atoms, an alkyleneoxyalkylene group having 2 to 30 carbon atoms, or an alkylene polyoxyalkylene group having 3 to 30 carbon atoms, X²¹ is an oxygen atom or a —C(═O)X²²L²²O— group, X²² is an oxygen atom or a —N(R^(x22))— group, R^(x22) is an alkyl group having 1 to 6 carbon atoms, and L²² is an alkylene group having 1 to 30 carbon atoms, an arylene group having 6 to 30 carbon atoms, an alkylene arylene group having 7 to 30 carbon atoms, an alkylene arylene alkylene group having 8 to 30 carbon atoms, an alkyleneoxyalkylene group having 2 to 30 carbon atoms, or an alkylene polyoxyalkylene group having 3 to 30 carbon atoms, in Formula (3), Z³¹ is an (n+1)-valent organic group having 2 to 30 carbon atoms, and Z³² is an (m+1)-valent organic group having 2 to 100 carbon atoms.
 6. The water dispersion of gel particles according to claim 4, wherein X²¹ in Formula (2) is a —C(═O)X²²L²²O— group.
 7. The water dispersion of gel particles according to claim 1, wherein the hydrophilic group is at least one selected from the group consisting of a carboxyl group, a salt of a carboxyl group, a sulfo group, a salt of a sulfo group, a sulfate group, a salt of a sulfate group, a phosphonic acid group, a salt of a phosphonic acid group, a phosphoric acid group, a salt of a phosphoric acid group, an ammonium salt group, a betaine group, and an alkyleneoxy group.
 8. The water dispersion of gel particles according to claim 1, wherein the three-dimensional crosslinked structure includes a structural unit represented by Formula (W),

R^(W1) in Formula (W) represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, W¹ in Formula (W) represents a carboxyl group, a salt of the carboxyl group, a —C(═O)NH—R^(W2)—SO₃H group, a salt of a —C(═O)NH—R^(W3)—SO₃H group, a —C(═O)NH—R^(W4)—OSO₃H group, a salt of a —C(═O)NH—R^(W5)—OSO₃H group, or a —C(═O)O—(R^(W6)O)_(nw)—R^(W7) group, and R^(W2), R^(W3), R^(W4), R^(W5), and R^(W6) each independently represent an alkylene group having 1 to 10 carbon atoms, R^(W7) represents an alkyl group having 1 to 10 carbon atoms, and nw represents an integer of 1 to
 200. 9. The water dispersion of gel particles according to claim 1, wherein the gel particles further include a polymerizable monomer.
 10. The water dispersion of gel particles according to claim 9, wherein the polymerizable monomer is a (meth)acrylate monomer.
 11. The water dispersion of gel particles according to claim 1, wherein solubility of the photopolymerization initiator in water is 1.0 mass % or less at 25° C.
 12. The water dispersion of gel particles according to claim 1, wherein the photopolymerization initiator is an acylphosphine oxide compound.
 13. The water dispersion of gel particles according to claim 1, wherein the gel particles further include a sensitizer.
 14. The water dispersion of gel particles according to claim 1, which is used for ink jet recording.
 15. The water dispersion of gel particles according to claim 1, wherein a total solid content of the gel particles is 50 mass % or greater with respect to a total solid content of the water dispersion.
 16. The water dispersion of gel particles according to claim 1, wherein the three-dimensional crosslinked structure includes a structure of a reaction product between water and an isocyanate group-containing polymer including the structural unit represented by Formula (1) and an isocyanate group.
 17. A method of producing the water dispersion of gel particles according to claim 16, comprising: preparing an isocyanate group-containing polymer including the structural unit represented by Formula (1) and an isocyanate group, obtaining an emulsion by mixing an oil phase component including the isocyanate group-containing polymer, the photopolymerization initiator, and an organic solvent, and a water phase component including water and performing emulsification, and obtaining the water dispersion of gel particles by heating the emulsion to allow the isocyanate group-containing polymer and water to react with each other.
 18. An image forming method comprising: applying the water dispersion of gel particles according to claim 1 to a recording medium; and irradiating the water dispersion of gel particles applied to the recording medium with active energy rays.
 19. The water dispersion of gel particles according to claim 1, wherein the gel particles have a polymerizable group. 